'Belong' in the Bible

They went out from us [seeming at first to be Christians], but they were not really of us [because they were not truly born again and spiritually transformed]; for if they had been of us, they would have remained with us; but they went out [teaching false doctrine], so that it would be clearly shown that none of them are of us.

Little children (believers, dear ones), you are of God and you belong to Him and have [already] overcome them [the agents of the antichrist]; because He who is in you is greater than he (Satan) who is in the world [of sinful mankind].