For there are three that bear witness in heaven: the Father, the Word, and the Holy Spirit; and these three are one.
And there are three that bear witness on earth: the Spirit, the water, and the blood; and these three agree as one.
References for 1 John 5:8
If we receive the witness of men, the witness of God is greater; for this is the witness of God which He has testified of His Son.
References for 1 John 5:9
He who believes in the Son of God has the witness in himself; he who does not believe God has made Him a liar, because he has not believed the testimony that God has given of His Son.
And this is the testimony: that God has given us eternal life, and this life is in His Son.
He who has the Son has life; he who does not have the Son of God does not have life.
These things I have written to you who believe in the name of the Son of God, that you may know that you have eternal life, and that you may continue to believe in the name of the Son of God.
References for 1 John 5:13
Now this is the confidence that we have in Him, that if we ask anything according to His will, He hears us.
And if we know that He hears us, whatever we ask, we know that we have the petitions that we have asked of Him.
If anyone sees his brother sinning a sin which does not lead to death, he will ask, and He will give him life for those who commit sin not leading to death. There is sin leading to death. I do not say that he should pray about that.
All unrighteousness is sin, and there is sin not leading to death.