6 If we read, "Cursed of God is every one that hangs on a tree," the addition of the words "of God" creates no difficulty. For had not God hated sin and our death, He would not have sent His Son to bear and to abolish it. And there is nothing strange in God's cursing what He hates. For His readiness to give us the immortality which will be had at the coming of Christ, is in proportion to the compassion with which He hated our death when it hung on the cross at the death of Christ.
And if Moses curses every one that hangs on a tree, it is certainly not because he did not foresee that righteous men would be crucified, but rather because He foresaw that heretics would deny the death of the Lord to be real, and would try to disprove the application of this curse to Christ, in order that they might disprove the reality of His death. For if Christ's death was not real, nothing cursed hung on the cross when He was crucified, for the crucifixion cannot have been real.
Moses cries from the distant past to these heretics: Your evasion in denying the reality of the death of Christ is useless. Cursed is every one that hangs on a tree; not this one or that, but absolutely every one. What! The Son of God? Yes, assuredly. This is the very thing you object to, and that you are so anxious to evade. You will not allow that He was cursed for us, because you will not allow that He died for us. Exemption from Adam's curse implies exemption from his death.
But as Christ endured death as man, and for man; so also, Son of God as He was, ever living in His own righteousness, but dying for our offenses, He submitted as man, and for man, to bear the curse which accompanies death. And as He died in the flesh which He took in bearing our punishment, so also, while ever blessed in His own righteousness, He was cursed for our offenses, in the death which He suffered in bearing our punishment. And these words "every one" are intended to check the ignorant officiousness which would deny the reference of the curse to Christ, and so, because the curse goes along with death, would lead to the denial of the true death of Christ.
Source: Reply to Faustus the Manichaean (New Advent)