1 If ye remember, brethren, yesterday we closed our sermon at this sentence, which without doubt behooved and does behoove to abide in your heart, seeing it was the last ye heard. “My little children, let us not love only in word and in tongue; but in deed and in truth.” Then he goes on: “And herein we know that we are of the truth, and assure our hearts before Him.” “For if our heart think ill of us, God is greater than our heart, and knows all things.” He had said, “Let us not love only in word and in tongue, but in work and in truth:” we are asked, In what work, or in what truth, is he known that loves God, or loves his brother?
Above he had said up to what point charity is perfected: what the Lord says in the Gospel, “Greater love than this has no man, that one lay down his life for his friends,” this same had the apostle also said: “As He laid down His life for us, we ought also to lay down our lives for the brethren.” This is the perfection of charity, and greater can not at all be found. But because it is not perfect in all, and that man ought not to despair in whom it is not perfect, if that be already born which may be perfected: and of course if born, it must be nourished, and by certain nourishments of its own must be brought unto its proper perfection: therefore, we have asked concerning the commencement of charity, where it begins, and there have straightway found: “But whoso has this world's goods, and sees his brother have need, and shuts up his bowels of compassion from him, how dwells the love of the Father in him?” Here then has this charity, my brethren, its beginning: to give of one's superfluities to him that has need to him that is in any distress; of one's temporal abundance to deliver his brother from temporal tribulation. Here is the first rise of charity. This, being thus begun, if you shall nourish with the word of God and hope of the life to come, you will come at last unto that perfection, that you shall be ready to lay down your life for your brethren.
Source: Homilies on the First Epistle of John (New Advent)