A.T. Robertson Commentary 1 John 5:11

"And the witness is this, that God gave unto us eternal life, and this life is in his Son." — 1 John 5:11 (ASV)

That God gave (οτ εδωκεν ο θεος). Declarative οτ in apposition with μαρτυρια as in verse 14; John 3:19. Note aorist active indicative εδωκεν (from διδωμ) as in 3:23f. , the great historic fact of the Incarnation (John 3:16), but the perfect δεδωκεν in 1 John 3:1 to emphasize the abiding presence of God's love.

Eternal life (ζωην αιωνιον). Anarthrous emphasizing quality, but with the article in 1:2.

In his Son (εν τω υιω αυτου). This life and the witness also. This is why Jesus who is life (John 14:6) came to give us abundant life (John 10:10).