71 If then He said, My God, My God, why have You forsaken Me, and Father, into Your hands I commend My Spirit, that we might be sure that He did die, was not this, in His care for our faith, rather a scattering of our doubts, than a confession of His weakness? When He was about to restore Lazarus, He prayed to the Father: but what need had He of prayer, Who said, Father, I thank You, that You have heard Me; and I know that You hear Me always, but because of the multitude I said it, that they may believe that You sent Me ? He prayed then for us, that we may know Him to be the Son; the words of prayer availed Him nothing, but He said them for the advancement of our faith.
He was not in want of help, but we of teaching. Again He prayed to be glorified; and immediately was heard from heaven the voice of God the Father glorifying Him: but when they wondered at the voice, He said, This voice has not come for My sake, but for your sakes. The Father is besought for us, He speaks for us: may all this lead us to believe and confess! The answer of the Glorifier is granted not to the prayer for glory, but to the ignorance of the bystanders: must we not then regard the complaint of suffering, when He found His greatest joy in suffering, as intended for the building up of our faith?
Christ prayed for His persecutors, because they knew not what they did. He promised Paradise from the cross, because He is God the King. He rejoiced upon the cross, that all was finished when He drank the vinegar, because He had fulfilled all prophecy before He died. He was born for us, suffered for us, died for us, rose again for us. This alone is necessary for our salvation, to confess the Son of God risen from the dead: why then should we die in this state of godless unbelief? If Christ, ever secure of His divinity, made clear to us His death, Himself indifferent to death, yet dying to assure that it was true humanity that He had assumed: why should we use this very confession of the Son of God that for us He became Son of Man and died as the chief weapon to deny His divinity?
Source: On the Trinity (New Advent)