1 John 4:7

Beloved, let its love one another
The apostle having finished what he proposed to say concerning the trying of spirits, returns to his former exhortation to brotherly love, and which comes with fresh force and strength; for since worldly men follow, hear, embrace, and cleave to the false teachers; such as are of God, and on the side of truth, should love one another, and their faithful ministers, and stand fast in one spirit by the truths of the Gospel, in opposition to every error:

for love is of God:
to love one another is the command of God, it is his revealed will, and is well pleasing in his sight; it comes from him, is a gift of his grace, and a fruit of his Spirit, and which he teaches regenerate ones to exercise:

and everyone that loveth
God, as the Alexandrian copy reads, or Christ, and the saints, who seem to be particularly meant:

is born of God;
for love to the brethren is an evidence of regeneration; (See Gill on 1 John 3:14);

and knoweth God;
he knows God in Christ, and therefore loves those who have the grace of God in them, and the image of Christ upon them; he knows the mind and will of God, being taught of God to love the brethren; and he knows the love of God, and has had an experience of the grace of God, which influences him to love the saints.