Synopsis of the Books of the Bible, by John Nelson Darby, [1857-62], at sacred-texts.com
The Lord afterwards gives the substance of the whole law, as the principle of blessing between the creature and God, and that which formed the touchstone for the heart in the rejection of Christ. I say for the heart, because the trial was really there, although it was in the understanding that it appeared. Even when there were really orthodox principles (Christ being rejected), the heart that was not attached to His Person could not follow Him in the path to which His rejection led. The system of God's counsels which depended on that rejection was a difficulty. Those who were attached to His Person followed Him, and found themselves in it, without having well understood it beforehand. Thus the Lord gives the pith of the law the whole law as essentially divine instruction and the point at which the counsels of God are transplanted into the new scene, where they will be fulfilled apart from the wickedness or ill will of man. So that in these few Verses (Mar 12:28-37), the law and the Son of David are presented, and the latter taking His place as Son of man the Lord at the right hand of God. This was the secret of all that was going on. The union of His body, the assembly, with Himself was all that remained behind. Only in Mark the Prophet recognises the moral condition, under the law, that tends towards entrance into the kingdom (Mar 12:34). This scribe had the spirit of understanding.
The picture of the condition that would bring in judgment, which we find in Matthew 23, is not given here (see Synopsis about Matthew 23). It was not His subject. Jesus, still as the Prophet; warns His disciples morally; but the judgment of Israel, for rejecting the Son of David, is not here before His eyes in the same manner (that is to say, it is not the subject of which the Holy Ghost is here speaking). The real character of the scribes' devoutness is pointed out, and the disciples are warned against them. The Lord makes them feel also what it is that, in the eyes of God, gives true value to the offerings that were brought to the temple.
That is man under the old covenant, flesh under divine requirement, and no fruit to grow on it for ever.