From that time Jesus began to preach, and to say: Do penance, for the kingdom of heaven is at hand.
 And seeing the multitudes, he went up into a mountain, and when he was set down, his disciples came unto him.  And opening his mouth, he taught them, saying:...
Now and forever. Amen.
You may have noticed that I didn't post the whole text from Matthew 5-7. I decided quoting all three chapters here would be excessive, so I elected to simply quote the opening text. If you would like to read to full text, please do!
I had to make a decision regarding this reflection. The proclamation of the Kingdom was really the majority of Christ's ministry. Mixed in with this, He does a lot of healing, and casting out demons, etc. But, most of His actual teachings are about the Kingdom. Well, that's three years worth of teachings, and a lot of text to cover.
I made the decision to focus mainly on His Sermon on the Mount. I feel this is really the core of His teachings, and we can get a really good understanding of what He was proclaiming by understanding the sermon He gave on the mount. These teachings include the Beautitudes, His teachings on justice, how to pray (the Lord's Prayer), His teachings on judgement, and the need for a sound foundation of Faith.
I will do my best to get to the heart of these teachings without making an excessively long post.
1. Blessed are the poor in spirit: for theirs is the kingdom of heaven.
2. Blessed are the meek: for they shall possess the land.
3. Blessed are they that mourn: for they shall be comforted.
4. Blessed are they that hunger and thirst after justice: for they shall have their fill.
5. Blessed are the merciful: for they shall obtain mercy.
6. Blessed are the clean of heart: for they shall see God.
7. Blessed are the peacemakers: for they shall be called children of God.
8. Blessed are they that suffer persecution for justice' sake: for theirs is the kingdom of heaven.
Blessed are ye when they shall revile you, and persecute you, and speak all that is evil against you, untruly, for my sake: Be glad and rejoice, for your reward is very great in heaven. For so they persecuted the prophets that were before you. You are the salt of the earth. But if the salt lose its savour, wherewith shall it be salted? It is good for nothing any more but to be cast out, and to be trodden on by men. You are the light of the world. A city seated on a mountain cannot be hid. Neither do men light a candle and put it under a bushel, but upon a candlestick, that it may shine to all that are in the house. So let your light shine before men, that they may see your good works, and glorify your Father who is in heaven.
These are the 8 beatitudes of Our Lord. The first thing I want to point out is that the first and the eighth beatitudes mention as their reward, "theirs is the kingdom of heaven." Let these be "bookends," so that it is understood that all that comes in between is about the Kingdom, that the rewards of these beatitudes is heavenly in nature.
Now, rather than exposing the meaning behind each beatitude, I want to instead draw out the underlying common threads that they share. There are two that I want to point out. The first is that Jesus is turning the traditional understanding of God's blessings on its head, and the second is one that I've already mentioned: that God's blessings are firstly heavenly in nature, and earthly second.
The traditional understanding of God's blessings is something like: being in good health, owning land and property, having wealth, being well respected in the community, gaining victory in war, all of which comes from being obedient to the Law. Disobedience to the Law gains God's curses, which include things like, being overthrown in war, losing your wealth, getting sick with disease, like leprosy, losing your family, being looked down on by society, etc.
Here, Jesus is turning all of that on its head. Be poor in spirit (do not seek after wealth), be meek (control your passions), mourn, desire righteousness, be merciful, be pure of heart, be peacemakers, do not flee suffering and persecution. These are what make you blessed, not the material gain you may have.
And this leads well into the second part: the blessings God bestows for these beatitudes, which are heavenly in nature, rather than earthly, as was the traditional understanding. God blesses us with the Kingdom of Heaven, with possession of the earth (eschatologically), comfort, justice and righteousness, mercy, friendship with God (seeing His face), and adoption by God (children of God). These are the true blessings He bestows on us.
Bottom line: our righteous interior actions and dispositions will be rewarded with heavenly blessings.
Jesus then teaches a new kind of Justice. He prefaces these teachings by saying "unless your justice abound more than that of the scribes and Pharisees, you shall not enter into the kingdom of heaven." This teaching comes out of His teaching on the beatitudes, and is consonant with them. He is here teaching us to go beyond the justice of our actions, but to have a right interior life and disposition. This is why He repeatedly calls the scribes and Pharisees hypocrites, because their exterior lives were not integrated with their interior lives. They were obedient to the Law to a T, but interiorly, they did not abide by the spirit of that same Law.
So, what does Jesus teach here?
"You have heard that it was said to them of old: Thou shalt not kill. And whosoever shall kill shall be in danger of the judgment. But I say to you, that whosoever is angry with his brother, shall be in danger of the judgment."
"You have heard that it was said to them of old: Thou shalt not commit adultery. But I say to you, that whosoever shall look on a woman to lust after her, hath already committed adultery with her in his heart."
"And it hath been said, whosoever shall put away his wife, let him give her a bill of divorce. But I say to you, that whosoever shall put away his wife, excepting for the cause of fornication, maketh her to commit adultery: and he that shall marry her that is put away, committeth adultery."
"Again you have heard that it was said to them of old, Thou shalt not forswear thyself: but thou shalt perform thy oaths to the Lord.  But I say to you not to swear at all."
"You have heard that it hath been said, An eye for an eye, and a tooth for a tooth.  But I say to you not to resist evil [that is, be patient under injury]."
"You have heard that it hath been said, Thou shalt love thy neighbour, and hate thy enemy.  But I say to you, Love your enemies."
These teachings on Justice go beyond the exterior life, but enter into our interior lives. The purpose of the Law was to free Israel, as a people. What was the context of the Law, when it was given? God had just freed the Hebrews from Egypt. His first action after freeing them was to give them the Law. This can only be understood correctly if it is understood as a single action of freedom. We tend of thing of laws as restricting our freedom, but actually they enhance our freedom.
In particular, the Law was intended to free the Hebrews from the sinful culture they had learned from Egypt. Instead, over time, the Law became a thing of oppression, and rather than obedience for the sake of righteousness, it was obedience for the sake of obedience, and the hypocrisy was that they desired unrighteousness.
Jesus is teaching us here that these Laws that we are familiar with from the Patriarchs are intended to direct us toward a deeper kind of righteousness, that our interior lives are integrated with our exterior lives. If we are not to commit adultery, then we should not even desire adultery in our hearts. That's really the point. If we are not to kill, then we should not even desire to kill, should not harbor hatred in our hearts. That's really the point.
Again, Jesus is pointing us to deeper truths. The Law was meant to transform us inwardly, not simply to be practiced outwardly.
In continuity with these teachings, Jesus teaches us to pray "in secret." Again, the focus here is not on outward appearances, but on interior authenticity, integrity between our hearts and our actions. And in this secrecy, He teaches us to pray:
"Our Father who art in heaven, hallowed be thy name. Thy kingdom come. Thy will be done on earth as it is in heaven. Give us this day our supersubstantial bread. And forgive us our debts, as we also forgive our debtors. And lead us not into temptation. But deliver us from evil. Amen."
Thy will be done on earth as it is in heaven. This is essentially Jesus' teaching here. Supersubstantial bread speaks about a "hidden" substance, a continuation of Jesus' teaching. If we are unwilling, in our hearts, to forgive, then we do not deserve forgiveness. And don't just keep us from committing evil action, keep us from the very temptation of it. And deliver us from [the evil one], a reminder that our true enemy is hidden (a spirit).
Jesus completes this teaching on prayer and justice and blessedness by teaching us that "For where thy treasure is, there is thy heart also." So, we must transform our hearts such that God alone is our treasure. This is the heart of His teaching. The Kingdom of Heaven is for those who treasure it in their hearts. "Seek ye therefore first the kingdom of God, and his justice, and all these things shall be added unto you."
"Judge not, that you may not be judged, For with what judgment you judge, you shall be judged: and with what measure you mete, it shall be measured to you again."
Jesus goes on to teach us about right judgment. Ah, the dreaded "judge not" line. Except, this teaching isn't about not judging people at all! It's a warning about making sure you judge things and people properly. Be careful when you judge, because if you're guilty of the same fault, then you will be judged as harshly for that same fault as how you judged others for it.
However, Jesus does intend for us to use right judgement. He continues His teaching: "Give not that which is holy to dogs; neither cast ye your pearls before swine, lest perhaps they trample them under their feet, and turning upon you, they tear you." You can only know what a "dog" is, or what a "swine" is, with right judgment. And yes, Jesus is using colorful metaphor here to speak about certain kinds of people.
But, then we also have an odd teaching thrown in here, and it almost seems out of place. He says, "Ask, and it shall be given you: seek, and you shall find: knock, and it shall be opened to you. For every one that asketh, receiveth: and he that seeketh, findeth: and to him that knocketh, it shall be opened." It is only when we understand that this is stated in continuity with His teaching on right judgment that we see how this teaching fits here. Jesus is telling us that whatever we have discerned our need to be, with right judgment, and we ask that this need be fulfilled, this request will be granted to us. This teaching is not about asking for just anything. It's about asking for the right things.
This gives us the golden rule, which He teaches here, "All things therefore whatsoever you would that men should do to you, do you also to them. For this is the law and the prophets."
"Enter ye in at the narrow gate: for wide is the gate, and broad is the way that leadeth to destruction, and many there are who go in thereat. How narrow is the gate, and strait is the way that leadeth to life: and few there are that find it!"
This teaching on judgment, right judgment, grows out of Jesus earlier teachings on a righteous interior disposition. Without a right interior life, one cannot properly discern. We are called to properly discern our own sins, so as to avoid condemning others for the same sins. We are called to judge others, so as not to allow them to trample what is Holy, we are called to properly discern our own spiritual needs, so we know what to ask God for in prayer, and we must discern properly what behavior is good, so that we may do it, and that others may do likewise by our example. Doing all of this, we may find the narrow way to Heaven. If we do not judge rightly, we will walk the broad way.
A Sure Foundation
"Not every one that saith to me, Lord, Lord, shall enter into the kingdom of heaven: but he that doth the will of my Father who is in heaven, he shall enter into the kingdom of heaven."
Our foundation of Faith must be secure. Our foundation must be based on these teachings of Jesus, to hear them and obey them. We must transform our inner dispositions to align with the beatitudes. Out of this beatified disposition, we must enter into a more worthy righteousness, a more Godly justice, one based on deeper fundamental truths, an inner justice that is a fulfillment of the Law. We must pray rightly, seeking God and His Kingdom first, before all things, and with this rightly ordered heart, we must make right judgements about ourselves and about those around us. Obedience to these teachings is the sure foundation of our Faith.
"Every one therefore that heareth these my words, and doth them, shall be likened to a wise man that built his house upon a rock. And the rain fell, and the floods came, and the winds blew, and they beat upon that house, and it fell not, for it was founded on a rock. And every one that heareth these my words, and doth them not, shall be like a foolish man that built his house upon the sand, And the rain fell, and the floods came, and the winds blew, and they beat upon that house, and it fell, and great was the fall thereof."