"The moral law doth for ever bind all, as well justified persons as others, to the obedience thereof, and that not only in regard of the matter contained in it, but also in respect of the authority of God the Creator, who gave it; neither doth Christ in the Gospel any way dissolve, but much strengthen this obligation." Baptist Confession 1689, 19.5
When Jesus says, "You have heard it said...but I say unto you..." in Matthew 5-7, He is not doing away with the Law (specifically, the 10 Commandments). Rather, He is exposing the legalism of the Pharisees. Often times, the Sermon on the Mount is a chief text used by many to make the claim that Jesus brings in a new law, and does away with the moral law of the Old Testament. A brief study of the Pharisaical teaching and method of the day, of adding rules upon rules to God's perfect law, which occurred in the inter-testamental period, will show the context for Jesus' teaching. Jesus is not seeking to abolish the forever binding moral law of God (summarized in the Decalogue), but rather, He is teaching on how the Law is applied, and how it needs to be separated from the legalism of the religious leaders of the day.
In our day, preaching grace has often meant that many resort either to saying the the entire Old Testament law is done away with, or it has meant calling the adherence to the Law "legalism". (This is most often seen in the keeping of Sabbath). How ironic. Jesus is upholding Law over against legalism, and now many today are using those same passages to call Law legalism. We must preach bold grace...and yes, there are times we may sound antinomian because we preach grace to the deepest of sins and we preach repentance boldly, inviting any to come. "Such is the provision which God hath made through Christ in the covenant of grace for the preservation of believers unto salvation; that although there is no sin so small but it deserves damnation; yet there is no sin so great that it shall bring damnation on them that repent; which makes the constant preaching of repentance necessary." Baptist Confession 1689, 15.5
However, we must not "be" antinomian" in casting off obedience to God's law as a way of glorifying the God Who saved those who broke His righteous law.
I must boldly preach grace, and monergistic grace at that. God saves me...He sanctifies me...he ordains good works for me to do (Eph 2:10). I can boldly proclaim grace for any sin, but I must also proclaim that true faith and repentance are met with obedience to God's law as lifestyle, imperfect as it may be.
"Although true believers be not under the law as a covenant of works, to be thereby justified or condemned, yet it is of great use to them as well as to others, in that as a rule of life, informing them of the will of God and their duty, it directs and binds them to walk accordingly; discovering also the sinful pollutions of their natures, hearts, and lives, so as examining themselves thereby, they may come to further conviction of, humiliation for, and hatred against, sin; together with a clearer sight of the need they have of Christ and the perfection of his obedience; it is likewise of use to the regenerate to restrain their corruptions, in that it forbids sin; and the threatenings of it serve to shew what even their sins deserve, and what afflictions in this life they may expect for them, although freed from the curse and unallayed rigour thereof. The promises of it likewise shew them God's approbation of obedience, and what blessings they may expect upon the performance thereof, though not as due to them by the law as a covenant of works; so as man's doing good and refraining from evil, because the law encourageth to the one and deterreth from the other, is no evidence of his being under the law and not under grace. Neither are the aforementioned uses of the law contrary to the grace of the Gospel, but do sweetly comply with it, the Spirit of Christ subduing and enabling the will of man to do that freely and cheerfully which the will of God, revealed in the law, requireth to be done."
Baptist Confession 1689, 19.6-7
Baptist Confession 1689, 19.6-7
Christians can be like the Psalmist who "delights in the Law of the Lord." I delight as one who has a record of obedience because of Christ's work, and as one who sees the beauty of the Law as a means of living for the God who saves.--the God who saves a law-breaker like me. Legalism is adding to His law, it is not seeking to keep His law by His grace...