By this we know that we love the children of God: when we love God and keep His commandments.
Observe here, That the sincerity of our love to the children of God is best discovered by our love to God, and obedience to his commands. Quest. 1. What kind of love is required towards the children of God? Ans. A love of esteen, a love of desire, a love of delight, and a love of service and beneficence. Quest. 2.
Verse 2. By this we know that we love the children of God, etc. This is repeating the same truth in another form. "As it is universally true that if we love him who has begotten us, we shall also love his children, or our Christian brethren, so it is true also that if we love his children it will follow that we love him."...
By--Greek, "In." As our love to the brethren is the sign and test of our love to God, so (John here says) our love to God (tested by our "keeping his commandments") is, conversely, the ground and only true basis of love to our brother.