And since Celsus, although professing to know all about the Gospel, reproaches the Saviour because of His sufferings, saying that He received no assistance from the Father, or was unable to aid Himself; we have to state that His sufferings were the subject of prophecy, along with the cause of them; because it was for the benefit of mankind that He should die on their account, and should suffer stripes because of His condemnation. It was predicted, moreover, that some from among the Gentiles would come to the knowledge of Him (among whom the prophets are not included); and it had been declared that He would be seen in a form which is deemed dishonourable among men.
The words of prophecy run thus: “Lo, my Servant shall have understanding, and shall be exalted and glorified, and raised exceedingly high. In like manner, many shall be astonished at You; so Your form shall be in no reputation among men, and Your glory among the sons of men. Lo, many nations shall marvel because of Him; and kings shall close their mouths: because they, to whom no message about Him was sent, shall see Him; and they who have not heard of Him, shall have knowledge of Him.” “Lord, who has believed our report?
And to whom was the arm of the Lord revealed? We have reported, as a child before Him, as a root in a thirsty ground. He has no form nor glory; and we beheld Him, and He had not any form nor beauty: but His appearance was without honour, and deficient more than that of all men. He was a man under suffering, and who knew how to bear sickness: because His countenance was averted, He was treated with disrespect, and was made of no account. This man bears our sins, and suffers pain on our behalf; and we regarded Him as in trouble, and in suffering, and as ill-treated.
But He was wounded for our sins, and bruised for our iniquities. The chastisement of our peace was upon Him; by His stripes we were healed. We all, like sheep, wandered from the way. A man wandered in his way, and the Lord delivered Him on account of our sins; and He, because of His evil treatment, opens not His mouth. As a sheep was He led to slaughter; and as a lamb before her shearer is dumb, so He opens not His mouth. In His humiliation His judgment was taken away. And who shall describe His generation? Because His life is taken away from the earth; because of the iniquities of My people was He led unto death.”
Source: Against Celsus (New Advent)