Thomas Aquinas

“ A precept is fulfilled perfectly, when the end intended by the author of the precept is reached; yet it is fulfilled, imperfectly however, when although the end intended by its author is not reached, nevertheless the order to that end is not departed from. Thus if the commander of an army order his soldiers to fight, his command will be perfectly obeyed by those who fight and conquer the foe, which is the commander's intention; yet it is fulfilled, albeit imperfectly, by those who fight without gaining the victory, provided they do nothing contrary to military discipline. ”

“ The order of those four things we have to love out of charity is expressed in Holy Writ. For when we are commanded to love God with our "whole heart," we are given to understand that we must love Him above all things. When we are commanded to love our neighbor "as ourselves," the love of self is set before love of our neighbor. ”

“ Hence a thing is a matter of precept, in so far as it is something due. Now a thing is due in two ways, for its own sake, and for the sake of something else. In every affair, it is the end that is due for its own sake, because it has the character of a good for its own sake: while that which is directed to the end is due for the sake of something else: thus for a physician, it is due for its own sake, that he should heal, while it is due for the sake of something else that he should give a medicine in order to heal. ”

“ As Augustine says (De Doctr. Christ. i, 23) , "though four things are to be loved out of charity, there was no need of a precept as regards the second and fourth," i.e. love of oneself and of one's own body. "For however much a man may stray from the truth, the love of himself and of his own body always remains in him." And yet the mode of this love had to be prescribed to man, namely, that he should love himself and his own body in an ordinate manner, and this is done by his loving God and his neighbor. ”

“ For whoever transgresses a precept does a wrong. But if man loves some one as much as he ought, and loves any other man more, he wrongs no man. Therefore he does not transgress the precept. Therefore the order of charity is not included in the precept. ”

“ Further, precepts are given in order to direct man in the way of salvation, according to Ps. 18:9: "The commandment of the Lord is lightsome, enlightening the eyes." Now it is useless to direct anyone to what is impossible. Therefore it is not impossible to fulfill this precept in this life.
On the contrary, Augustine says (De Perfect. Justit. viii) : "In the fulness of heavenly charity this precept will be fulfilled: Thou shalt love the Lord thy God," etc. For as long as any carnal concupiscence remains, that can be restrained by continence, man cannot love God with all his heart. ”

“ Thou shalt love thy neighbor as thyself."
I answer that, This precept is fittingly expressed, for it indicates both the reason for loving and the mode of love. The reason for loving is indicated in the word "neighbor," because the reason why we ought to love others out of charity is because they are nigh to us, both as to the natural image of God, and as to the capacity for glory. ”

“ Further, virtue consists not only in doing good but also in avoiding evil. Now we are led by the positive precepts to do good, and by the negative precepts to avoid evil. Therefore there ought to have been not only positive, but also negative precepts about charity; and so two precepts of charity are not sufficient. ”

“ If, therefore, any precepts were given about charity, they should have a place among the chief precepts which are those of the decalogue. But they have no place there. Therefore no precepts should be given about charity.
On the contrary, Whatever God requires of us is included in a precept. Now God requires that man should love Him, according to Dt. 10:12. Therefore it behooved precepts to be given about the love of charity, which is the love of God. ”

“ That perfection of charity to which the counsels are directed, is between the two perfections mentioned in the preceding reply: and it consists in man renouncing, as much as possible, temporal things, even such as are lawful, because they occupy the mind and hinder the actual movement of the heart towards God. ”

“ Even as the soldier who fights legitimately without conquering is not blamed nor deserves to be punished for this, so too he that does not fulfil this precept on the way, but does nothing against the love of God, does not sin mortally. ”

“ For an impure heart is withdrawn from loving God, on account of the passion that inclines it to earthly things; an evil conscience gives man a horror for God's justice, through fear of His punishments; and an untrue faith draws man's affections to an untrue representation of God, and separates him from the truth of God. ”

“ And yet we find that, for the sake of the laggards, special precepts were given about each act---about joy (Phil. 4:4) : "Rejoice in the Lord always"---about peace (Heb. 12:14) : "Follow peace with all men"---about beneficence (Gal. 6:10) : "Whilst we have time, let us work good to all men"---and Holy Writ contains precepts about each of the parts of beneficence, as may be seen by anyone who considers the matter carefully. ”