Catena Aurea on Matthew 22:34–40: Origen

Or otherwise; “With all thy heart,” that is, in all recollection, act, thought; “with all thy soul,” to be ready, that is, to lay it down for God’s religion; “with all thy mind,” bringing forth nothing but what is of God. And consider whether you cannot thus take the heart of the understanding, by which we contemplate things intellectual, and the “mind” of that by which we utter thoughts, walking as it were with the mind through each expression, and uttering it.

If the Lord had given no answer to the Pharisee who thus tempted Him, we should have judged that there was no commandment greater than the rest. But when the Lord adds, “This is the first and great commandment,” we learn how we ought to think of the commandments, that there is a great one, and that there are less down to the least. And the Lord says not only that it is a great, but that it is the first commandment, not in order of Scripture, but in supremacy of value.

They only take upon them the greatness and supremacy of this precept, who not only love the Lord their God, but add these three conditions. Nor did He only teach the first and great commandment, but added that there was a second like unto the first, “Thou shalt love thy neighbour as thyself:” But if “Whoso loveth iniquity hath hated his own soul,” [Ps 11:5] it is manifest that he does not love his neighbour as himself, when he does not love himself.

Aug., de Doctr. Christ., i, 30; see Rom 13:10: It is clear that every man is to be regarded as a neighbour, because evil is to be done to no man. Further, if every one to whom we are bound to shew service of mercy, or who is bound to shew it to us, be rightly called our neighbour, it is manifest that in this precept are comprehended the holy Angels who perform for us those services of which we may read in Scripture.

Whence also our Lord Himself would be called our neighbour; for it was Himself whom He represents as the good Samaritan, who gave succour to the man who was left half-dead by the way.