And this is the record - This is the sum, or the amount, of the testimony (μαρτυρία marturia) which God has given respecting him.
That God hath given to us eternal life - Has provided, through the Saviour, the means of obtaining eternal life. See the notes at John 5:24; John 17:2-3.
And this life is in his Son - Is treasured up in him, or is to be obtained through him. See the John 1:4; John 11:25; John 14:6 notes; Colossians 3:3 note.