Very clearly, the purpose throughout this entire passage is not at all to slacken any of the Ten Commandments. To the contrary. The emphasis here is irrebuttably to enjoin the observance of the Decalogue, especially by Christians, till the very end of world history. Indeed, several times here Jesus approves even of civil punishments against such transgressions of the Decalogue as are also crimes (cf. Matt. 5:21-22 & 5:23-26 etc.).
Mount Sinai the root of Jehovah-Jesus' Sermon on the Mount (Matt. 5:1-2)
When Jesus saw the crowds, He went up into THE MOUNTAIN just like Moses did at MOUNT SINAI.1 And when He sat down, His DISCIPLES came to Him.2 And, opening His mouth, He taught them and said both to His disciples and TO THE CROWDS:3
Jehovah-Jesus introduces His Moral Law (Matt. 5:3-12)
"Blessed are those whose own spirit is poor or who long for God's rich Spirit to fulfill THE RIGHTEOUSNESS OF THE LAW in them — for their's is the Kingdom of Heaven!4 Blessed are those who mourn for their sin, which is THE TRANSGRESSION OF THE LAW5 — for they shall be comforted when the Holy Comforter WRITES THE LAW OF GOD ON THEIR HEARTS!6 Blessed are the meek or those who subject themselves to GOD'S HOLY LAW — for they shall inherit the Earth!7 Blessed are those who hunger and thirst for righteousness and who desire to be LAWABIDING people — for they shall be contented and they SHALL NOT COVET but keep THE TENTH COMMANDMENT!8 Blessed are the merciful — for
1 Matt. 5:1, eis to horos = "into THE mountain," cf. Matt. 8:1. Note that Sinai too is called "THE mountain," Ex. 19:2,3,12-14,20 & 20:18 & 24:12-18 cf. Heb. 12:18-22. 2 Christ's Sermon on the Mount (like His previous enunciation of the Decalogue on Mount Sinai) is addressed not to Pharisees or to heathen in the first instance, but particularly to his disciples and hence to Christians, Matt. 5:2 and Luke 6:20f. Cf. however note 152 below. 3 The crowds were apparently also listening to the Sermon, and it would seem that they too consisted of believers, Matt. 5:1f cf. 4:17-5:2 & 7:28-8:1 & Luke 6:17-23, or at least consisted of those that claimed to believe in and were in fact physically following Jesus; cf. note 2. 4 Matt. 5:3 cf. Rom. 8:3,4. 5 Matt. 5:4a cf. I John 3:4. 6 Matt. 5:4b cf. Ezek. 36:25-27 & John 14:15-18,26 & 15:10,26 & Heb. 8:10f & 10:15-16. 7 Matt. 5:5 cf. Ps. 37:7-11,29-31. 8 Matt. 5:6 cf. Eccl. 7:29; Rom. 2:14-15; Eph. 4:24.
they shall obtain mercy or forgiveness of their own transgressions of THE LAW OF GOD!9 Blessed are the pure in heart or those who do NOT COMMIT ADULTERY but keep THE SEVENTH COMMANDMENT — for they shall see God!10 Blessed are the peacemakers or those who DO NOT MURDER but keep THE SIXTH COMMANDMENT11 — for they shall be called the children of God or righteous Christians!12 Blessed are they who are persecuted for the sake of righteousness on account of their loyalty to THE TEN COMMANDMENTS — for their's is the Kingdom of Heaven!13 Blessed are all of you14 when men shall revile you and transgress THE THIRD COMMANDMENT,15 and persecute you and transgress THE SIXTH COMMANDMENT,16 and shall say every evil thing against you falsely and transgress THE NINTH COMMANDMENT17 by calling you legalists — for My sake!18 Rejoice, and be exceedingly glad: great is your heavenly reward for your own good works of KEEPING THE MORAL LAW by God's grace out of gratitude to Him for His faithful mercy toward you!19 For in the same way, they also persecuted the prophets before you who preached and obeyed THE LAW OF GOD!20