1 John 5:2

2Byἐνthisτούτῳwe knowγινώσκομενthatὅτιwe loveἀγαπῶμενtheτὰchildrenτέκνατοῦof Godθεοῦ,whenὅταντὸνGodθεὸνwe loveἀγαπῶμενandκαὶtheτὰςcommandmentsἐντολὰςof Himαὐτοῦkeepποιῶμεν·

In this we know that we love the children of God, when we love God and keep His commandments.