Why must he be very man, and also perfectly righteous?
Because the justice of God requires that the same human nature which has sinned, should likewise make satisfaction for sin;1 and one, who is himself a sinner, cannot satisfy for others.2
Why must he in one person be also very God?
That he might, by the power of his Godhead3 sustain in his human nature,4 the burden of God's wrath;5 and might obtain for, and restore to us, righteousness and life.6
1 Ezek. 18:4, 20; Rom. 5:12, 15, 18; 1 Cor. 15:21; Heb. 2:14-16; 1 Pet. 3:18; Isa. 53:3-5, 10, 11.