Matthew 5:17-19 "If you think the law of Moses was crucial... wait till you get a load of the law of Christ."

Jesus emphasizes the importance of these defining statements (Matt. 5:3-10), by speaking about His relationship to the Law.  The Torah (law) was sure, and none of it would pass away without being fulfilled.  Therefore the words of Jesus, the one who brings the Torah to fulfillment...His words are even more sure and whoever neglects the least of them will be called least in the Kingdom of Heaven (Matt. 5:17-19).

Here is the principle, "if the lesser was authoritative, how much more will the greater be authoritative?" The Torah was steadfast in its entirety and to move beyond the binding nature of the Torah would require a dramatically new situation. Not a tidbit can pass until all is accomplished. How much more steadfast is the Word of God spoken to us through God's Son. The Gospel Commands of Jesus cut deeper than the Torah did.  They cut deep enough to get at the old nature of every disciple, carrying each of us along to the point of death...but those who are in Christ will not be hurt by the second death!   Even though these Gospel Commands will cut deeply, we are not to neglect them. The lesser Torah was not to be neglected and neither should the greater "commands of Christ" be neglected.  Several passages come to mind which use this way of thinking.
1) In Deuteronomy there is a principle which Paul will use in Romans: God, in the "lesser" law has adequately communicated all that we need to be obedient to Him. 

if you obey the LORD your God to keep His commandments and His statutes which are written in this book of the law, if you turn to the LORD your God with all your heart and soul. "For this commandment which I command you today is not too difficult for you, nor is it out of reach. "It is not in heaven, that you should say, 'Who will go up to heaven for us to get it for us and make us hear it, that we may observe it?' "Nor is it beyond the sea, that you should say, 'Who will cross the sea for us to get it for us and make us hear it, that we may observe it?' "But the word is very near you, in your mouth and in your heart, that you may observe it (Deut 30:10-14).

This principle is all the more present for the "greater" obedience of faith, in the New Testament.

For Christ is the end of the law for righteousness to everyone who believes. For Moses writes that the man who practices the righteousness which is based on law shall live by that righteousness. But the righteousness based on faith speaks as follows: "DO NOT SAY IN YOUR HEART, 'WHO WILL ASCEND INTO HEAVEN?' (that is, to bring Christ down), or 'WHO WILL DESCEND INTO THE ABYSS?' (that is, to bring Christ up from the dead)." But what does it say? "THE WORD IS NEAR YOU, IN YOUR MOUTH AND IN YOUR HEART"--that is, the word of faith which we are preaching, that if you confess with your mouth Jesus as Lord, and believe in your heart that God raised Him from the dead, you will be saved (Rom 10:4-9);

2) When speaking of the relationship between the word of God in the Old Testament and the word of God in the New Testament; The author of Hebrews emphasizes the transition from the lesser, to the greater.

God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world. And He is the radiance of His glory and the exact representation of His nature, and upholds all things by the word of His power. When He had made purification of sins, He sat down at the right hand of the Majesty on high, having become as much better than the angels, as He has inherited a more excellent name than they...(Heb 1:1-4).
For this reason we must pay much closer attention to what we have heard, so that we do not drift away from it. For if the word spoken through angels proved unalterable, and every transgression and disobedience received a just penalty, how will we escape if we neglect so great a salvation? After it was at the first spoken through the Lord, it was confirmed to us by those who heard, God also testifying with them, both by signs and wonders and by various miracles and by gifts of the Holy Spirit according to His own will (Heb 2:1-4).

3) James is concerned that the Christian pay special attention to the "kings law" by which we will be judged.  Just as the one who breaks one point in the Torah would be guilty of the whole, so those not paying attention to the "law of liberty" with its command of mercy, will be judged without mercy.

My brethren, do not hold your faith in our glorious Lord Jesus Christ with an attitude of personal favoritism...If, however, you are fulfilling the royal law according to the Scripture,(or you are fulfilling the King's law concerning the scripture:) "YOU SHALL LOVE YOUR NEIGHBOR AS YOURSELF," you are doing well. But if you show partiality, you are committing sin and are convicted by the law as transgressors. For whoever keeps the whole law and yet stumbles in one point, he has become guilty of all. For He who said, "DO NOT COMMIT ADULTERY," also said, "DO NOT COMMIT MURDER." Now if you do not commit adultery, but do commit murder, you have become a transgressor of the law. So speak and so act as those who are to be judged by the law of liberty. For judgment will be merciless to one who has shown no mercy; mercy triumphs over judgment (Jas. 2:1,8-13).

4) Peter speaks of the Gospel account being a more sure prophetic word than what has gone before. But this prophetic word must be heeded without giving in to false teachers. A principle carried over from when the inspired scriptures of the Old Testament were surrounded by the misleading messages of the false prophets.

For we have not followed cunningly devised fables, when we made known unto you the power and coming of our Lord Jesus Christ, but were eyewitnesses of his majesty. For he received from God the Father honour and glory, when there came such a voice to him from the excellent glory, This is my beloved Son, in whom I am well pleased. And this voice which came from heaven we heard, when we were with him in the holy mount. We have also a more sure word of prophecy ["more steadfast prophetic word," i.e. the gospel with its commands!]; whereunto ye do well that ye take heed, as unto a light that shineth in a dark place, until the day dawn, and the day star arise in your hearts: Knowing this first, that no prophecy of the scripture [or "prophetic scripture"] is of any private interpretation [or "origin"]. For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost. But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction (2Pe 1:16- 2:1).

In a related essay at the left, "progress in acts and in you", we see the author of Acts using the phrase "Word of God" in a dynamic way to refer to "God's prophetic word to the present situation" (similar to how we see it used throughout the Old Testament).  And the "present situation" is that time from Jesus' ascension until his "soon" return. So in Acts the phrase "word of God" would appear to stand for the Gospel, including the Gospel Commands, while The Old Testament is referred to as "the scriptures"or "the law". And so it is incumbent upon disciples, then and now, to acknowledge Jesus as the one who affirms the authority of the Law, fulfills the Law , and  replaces the Law for the faithful.  Jesus is the one who presently instructs and shepherds the remnant of  Israel.