14 “Whosoever shall confess that Jesus is the Son of God, God dwells in him and he in God.” Now we may say it in not many words; “Whosoever shall confess;” not in word but in deed, not with tongue but with the life. For many confess in words, but in deeds deny: “And we have known and believed the love which God has in us.” And again, by what have you come to know this? “Love is God.” He has already said it above, behold he says it again. Love could not be more exceedingly commended to you than that it should be called God.
Haply you were ready to despise a gift of God. And do you despise God? “Love is God: and he that dwells in love dwells in God, and God dwells in him.” Each mutually inhabites the other; He that holds, and he that is holden. You dwell in God, but that you may be holden: God inhabites you, but that He may hold you, lest you fall. Lest haply you imagine that you become an house of God in such sort as your house supports your flesh: if the house in which you are withdraw itself from under you, you fall, but if you withdraw yourself, God falls not.
When you forsake Him, He is none the less; when you have returned unto Him, He is none the greater. You are healed, on Him you will bestow nothing; you are made clean, you are new-made, you are set right: He is a medicine to the unhealthy, is a rule for the crooked, is light for the bedarkened, is an habitation for the deserted. All therefore is conferred on you: see that you imagine not that ought is conferred upon God by your coming unto Him: no, not so much as a slave. Shall God, forsooth, not have servants if you like not, if all like not?
God needs not the servants, but the servants need God: therefore says the Psalm, “I have said unto the Lord, you are my God.” He is the true Lord. And what says it? “For of my goods You have no need.” Thou needest the good you have by your servant. Your servant needs the good he has by you, that you may feed him; you also need the good you have by your servant, that he may help you. You can not draw water for yourself, canst not cook for yourself, canst not run before your horse, canst not tend your beast.
You see that you need the good you have by your servant, you need his attendance. Therefore you are not a true lord, while you have need of an inferior. He is the true Lord, who seeks nothing from us; and woe to us if we seek not Him! He seeks nothing from us: yet He sought us, when we sought not Him. One sheep had strayed; He found it, He brought it back on His shoulders rejoicing. And was the sheep necessary for the Shepherd, and not rather the Shepherd necessary for the sheep?— The more I love to speak of charity, the less willing am I that this epistle should be finished.
None is more ardent in the commending of charity. Nothing more sweet is preached to you, nothing more wholesome drunk by you: but only thus if by godly living ye confirm in you the gift of God. Be not ungrateful for His so great grace, who, though He had one Only Son, would not that He should be alone a Son; but, that He might have brethren, adopted unto Him those who should with Him possess life eternal.
Source: Homilies on the First Epistle of John (New Advent)