1 John 5:20
And we know that the Son of God has come and has given us understanding, so that we may know Him who is true; and we are in Him who is true — in His Son Jesus Christ. He is the true God and eternal life.
What it says
The Son of God has come and given understanding so believers may know the true God in His Son Jesus Christ.
What it is doing
This verse climaxes the chapter by fixing knowledge, eternal life, and truth in the Son.
In context
18We know that anyone born of God does not keep on sinning; the One who was born of God protects him, and the evil one cannot touch him. 19We know that we are of God, and that the whole world is under the power of the evil one. 20And we know that the Son of God has come and has given us understanding, so that we may know Him who is true; and we are in Him who is true — in His Son Jesus Christ. He is the true God and eternal life. 21Little children, keep yourselves from idols.