Why must the Redeemer be truly God?
That because of his divine nature his obedience and suffering would be perfect and effective; and also that he would be able to bear the righteous anger of God against sin and yet overcome death.
God raised him up, loosing the pangs of death, because it was not possible for him to be held by it.
Acts 2:24
The early church had the task of sorting out all types of misunderstandings about who Christ was. The result was the Chalcedonian Creed:
Therefore, following the holy fathers, we all with one accord teach men to acknowledge one and the same Son, our Lord Jesus Christ, at once complete in Godhead and complete in manhood, truly God and truly man, consisting also of a reasonable soul and body; of one substance with the Father as regards his Godhead, and at the same time of one substance with us as regards his manhood; like us in all respects, apart from sin; as regards his Godhead, begotten of the Father before the ages, but yet as regards his manhood begotten, for us men and for our salvation, of Mary the Virgin, the God-bearer; one and the same Christ, Son, Lord, Only-begotten, recognized in two natures, without confusion, without change, without division, without separation; the distinction of natures being in no way annulled by the union, but rather the characteristics of each nature being preserved and coming together to form one person and subsistence, not as parted or separated into two persons, but one and the same Son and Only-begotten God the Word, Lord Jesus Christ; even as the prophets from earliest times spoke of him, and our Lord Jesus Christ himself taught us, and the creed of the fathers has handed down to us.
Pastor Josh teaches us from John 5, explains this further, teaching what it means when Jesus refers to himself as the Son of Man: (originally preached on November 18th, 2018)
“…So Jesus is claiming to be the unique Son of Man who was granted everlasting dominion, ruling an eternal kingdom with all of the Glory of God. And at the same time as being God, who has eternal dominion, an eternal kingdom, and the worship of all peoples — He belongs to humanity! He’s born of a woman. He has walked where humans have walked. And it’s not one or the other of these, but its the combination of these features that make him uniquely qualified to judge. So Jesus will be the one who judges - but he won’t just judge as God, because he’s also human. He’s fully God, fully man. And as such he is uniquely qualified to judge us…”