4 Bible Verses about Certainty

We know that whoever has been begotten by God, does not sin; but he who is begotten by God, guards himself, and the wicked on does not lay hold on him. We know that we are of God, and that the whole world lies under the wicked one. Moreover, we know that the Son of God has come, and has given us understanding, that we might know him that is true; and we are in him that is true-in his Son Jesus Christ. This is the true God, and the eternal life.

By this, we know that we abide in him, and he in us, because he has given us of his Spirit.

And by this, we know that we have known him, if we keep his commandments. He who says, I have known him, and does not keep his commandments, is a liar, and the truth is not in this man. But whoever keeps his word, truly in this man the love of God is perfected. By this we know that we are in him.read more.
He who says he abides in him, ought, himself, also, so to walk even as he walked.

And this is the confidence which we have with him, that if we ask anything according to his will, he hearkens to us. And if we know that he hearkens to us, concerning whatever we ask; we know that we shall obtain the petitions which we have asked from him.