The Great Commentary of Cornelius à Lapide
1 John 1:13
These things I write unto you, that ye who believe in the name of the Son of God have eternal life. The Greek adds, that ye may believe in the name of the Son of God. But this seems to be tautologous. The name of the Son of God is put for the thing signified, the Son of God Himself. There is an allusion to his own Gospel (Joh 20:31): "These things are written that ye may believe that Jesus is the Son of God, and that believing ye may have life in His name."
S. John here reckons up three fruits of a living faith in Christ. The first, life eternal in this verse; the second, confidence of obtaining all things from God (ver. 14); the third is complete banishment of sin, and moral sinlessness (ver. 18). Ver. 14. And this is the confidenre, &c. Truly says S. Augustine, "Whatsoever we ask unprofitable for our salvation we do not ask in the name of the Saviour."
And we know : the Greek adds ε̉ὰν, i.e., if. This makes the words of the verse more connected: And if we know that He heareth us, whatsoever we shall ask, we know that we have the petitions which we have asked of Him.