Love is of God; God is Love.
I. "Love is of God." This does not mean merely that love comes from God and has its source in God, that He is the Author or Creator of it. All created things are of God, for by Him all things were made, and on Him they all depend. But love is not a created thing; it is a Divine property, a Divine affection; and it is of its essence to be communicative and begetting, to communicate itself and, as it were, beget its own likeness. "Love is of God." It is not merely of God as every good gift is of God. It is of God as being His own property, His own affection, His own love. (1) None but one born of God can thus love with the love which in this sense is of God; therefore one who so loves must needs be one who is born of God. (2) Being born of God implies knowing God. It is a knowledge of God altogether peculiar, belonging exclusively to the relation constituted by, and realised in, your being born of God. It is the very knowledge of God which His Son has His only-begotten Son, whom He sent into the world to manifest His love.
II. Every one that loveth knoweth God; he that loveth not knoweth not God: these are the antagonistic statements. The fact of a man not loving plainly proves that he knows not God; and his not knowing God explains and accounts for the fact of his not loving. How, indeed, can he know God know Him as being love? To know God thus, as being love, implies some measure of congeniality, sympathy, and fellowship. There must be community of heart and nature between Him and me. I must be "born of God." (1) We are to love as He loves His only-begotten Son. Our thus loving Him is one primary criterion and touchstone of our being born of God. (2) Then we are to love, as God loves it and because God loves it, the world which He sent His Son to save. We are to love thus one another, with what intensity of longing, like God's own longing and yearning, for one another's salvation, that all may turn and live.
R. S. Candlish, Lectures on First John,Part III., p. 104.
References: 1 John 4:7-10. Homilist,3rd series, vol. viii., p. 219. 1 John 4:7-11. N. Beach, Christian World Pulpit,vol. xxxii., p. 178. 1 John 4:7-16. Preacher's Monthly,vol. i., p. 444.