Love and Obedience
1John 5:2 By this we generally know that we characteristically love the children of God, when we characteristically love God and characteristically keep His commandments.
Jesus said, "Whoever has my commands and obeys them, he is the one who loves me." John 14:21a Christian love for God is applied through submission to God and obedience to his commands. And what is his primary command but to love one another. Loving the brethren and loving God go hand in hand.
Don't misread this as aorist. He is not saying that we know we love God's children at the particular instance in which we love God and at the instance we keep His commandments. Rather this is simply a truism correlating all three things. Loving God, loving God's children, and obeying God's commands go hand in hand, and not as a requirement, but rather as a description of those born of God. And thus such attributes taken together can be used to diagnose one's salvation status.