John Calvin on 1 John 5:9

9 If we receive the witness, or testimony, of men He proves, reasoning from the less to the greater, how ungrateful men are when they reject Christ, who has been approved, as he has related, by God; for if in worldly affairs we stand to the words of men, who may lie and deceive, how unreasonable it is that God should have less credit given to him, when sitting as it were on his own throne, where he is the supreme judge. Then our own corruption alone prevents us to receive Christ,, since he gives us full proof for believing in his power. Besides, he calls not only that the testimony of God which the Spirit imprints on our hearts, but also that which we derive from the water and the blood. For that power of cleansing and expiating was not earthly, but heavenly. Hence the blood of Christ is not to be estimated according to the common manner of men; but we must rather look to the design of God, who ordained it for blotting out sins, and also to that divine efficacy which flows from it.

1 John 5:9-12

9. — For this is the witness of God which he hath testified of his Son.

9. — Porro hoc est testimonium Dei, quod testificatus est de Filio suo.

10. He that believeth on the Son of God hath the witness in himself: he that believeth not God hath made him a liar; because he believeth not the record that God gave of his Son.

10. Qui credit in Filium Dei, habet testimonium in seipso; qui non credit Deo, mendacem facit eum; quia non credidit in testimonium quod testificatus est Deus de Filio suo.

11. And this is the record, that God hath given to us eternal life, and this life is in his Son.

11. Et hoc est testimonium, quod vitam aeternam dedit nobis Deus; et haec vita in Filio ejus est.

12. He that hath the Son hath life; and he that hath not the Son of God hath not life.

12. Qui habet Filium, habet vitam; qui non habet Filium Dei, vitam non habet.