John Calvin's Commentary on the Bible - 1 John 5:10
Verse 10 9For this is the witness, or testimony, of God The particle ὅτι does not mean here the cause, but is to be taken as explanatory; for the Apostle, after having reminded us that God deserves to be believed much more than men, now adds, that we can have no faith in God, except by believing in Christ, because God sets him alone before us and makes us to stand in him. He hence infers that we believe safely and with tranquil minds in Christ, because God by his authority warrants our faith.... read more
Adam Clarke's Commentary on the Bible - 1 John 5:13
That ye may know that ye have eternal life - I write to show your privileges - to lead you into this holy of holies - to show what believing on the Son of God is, by the glorious effects it produces: it is not a blind reliance for, but an actual enjoyment of, salvation; Christ living, working, and reigning in the heart. And that ye may believe - That is, continue to believe: for Christ dwells in the heart only by Faith, and faith lives only by Love, and love continues only by Obedience;... read more