And we have seen and do testify that the Father sent the Son to be the Saviour of the world.
And we - primarily, we apostles, Christ's appointed eye-witnesses to testify to the facts concerning Him. The internal evidence of the indwelling Spirit (1 John 4:13) is corroborated by external evidence of the eye-witnesses to the fact of the Father having "sent the Son to be the Saviour of the world."
Seen, х tetheametha (G2300)] - 'contemplated;' 'attentively beheld' (note, 1 John 1:1).
Sent - `hath sent:' not entirely past (aorist), but one of which the effects continue (perfect).