On the contrary, Augustine says (De Serm.  Dom. in Monte i, 1):  We should take note that, when He said:  “’He that heareth these My words,’ He indicates clearly that this sermon of the Lord is replete with all the precepts whereby a Christian’s life is formed.”

I answer that, As is evident from Augustine’s words just quoted, the sermon, which Our Lord delivered on the mountain, contains the whole process of forming the life of a Christian.  Therein man’s interior movements are ordered.  Because after declaring that his end is Beatitude; and after commending the authority of the apostles, through whom the teaching of the Gospel was to be promulgated, He orders man’s interior movements, first in regard to man himself, secondly in regard to his neighbor.

This he does in regard to man himself, in two ways, corresponding to man’s two interior movements in respect of any prospective action, viz. volition of what has to be done, and intention of the end.  Wherefore, in the first place, He directs man’s will in respect of the various precepts of the Law:  by prescribing that man should refrain not merely from those external works that are evil in themselves, but also from internal acts, and from the occasions of evil deeds.  In the second place He directs man’s intention, by teaching that in our good works, we should seek neither human praise, nor worldly riches, which is to lay up treasures on earth.

Afterwards He directs man’s interior movement in respect of his neighbor, by forbidding us, on the one hand, to judge him rashly, unjustly, or presumptuously; and, on the other, to entrust him too readily with sacred things if he be unworthy.

Lastly, He teaches us how to fulfil the teaching of the Gospel; viz. by imploring the help of God; by striving to enter by the narrow door of perfect virtue; and by being wary lest we be led astray by evil influences.  Moreover, He declares that we must observe His commandments, and that it is not enough to make profession of faith, or to work miracles, or merely to hear His words.

Reply Obj. 1:  Our Lord explained the manner of fulfilling those precepts which the Scribes and Pharisees did not rightly understand:  and this affected chiefly those precepts of the decalogue.  For they thought that the prohibition of adultery and murder covered the external act only, and not the internal desire.  And they held this opinion about murder and adultery rather than about theft and false witness, because the movement of anger tending to murder, and the movement of desire tending to adultery, seem to be in us from nature somewhat, but not the desire of stealing or bearing false witness.  They held a false opinion about perjury, for they thought that perjury indeed was a sin; but that oaths were of themselves to be desired and to be taken frequently, since they seem to proceed from reverence to God.  Hence Our Lord shows that an oath is not desirable as a good thing; and that it is better to speak without oaths, unless necessity forces us to have recourse to them.