Jn 8:28, Jn 13:18-19
In the Old Testament, God said that God would make the people of Israel know that God is the true God through Christ, the servant of God. (Isa 43:10)
Isa 43:10 Ye are my witnesses, saith the Lord, and my servant whom I have chosen: that ye may know and believe me, and understand that I am he: before me there was no God formed, neither shall there be after me.
Jesus is the true witness of God. (John 8:28)
John 8:28 Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am he, and that I do nothing of myself; but as my Father hath taught me, I speak these things.
Jesus is the true servant of God, who accomplished the work of Christ, which God commanded, through death. (John 13:18-19)
John 13:18 I speak not of you all: I know whom I have chosen: but that the scripture may be fulfilled, He that eateth bread with me hath lifted up his heel against me. 19 Now I tell you before it come, that, when it is come to pass, ye may believe that I am he.