Though this is conventional thinking by evangelicals, I, and other theologically solid believers, believe it is in error.
The Father never left the Son - the proof is II Corin. 5:19, “God was in Christ reconciling the world to Himself....”....the Father was with Him and in Him through the whole transaction of the cross.
What our Lord Jesus lost, for the first and only time in all eternity - which is why it was such a total shock that he would cry out with these words - was the SENSE and AWARENESS of His Father’s presence......due to His humanity taking on the sin(s) of the world.
The Father actually has no problem with sin causing Him to be separated from the sinner - else no sinner would ever be saved. His holiness is not touched by sin - it either consumes it or it is dealt with by the shed blood of the Lamb of God.
Else we who are yet sinners, saved by grace, could never enter His presence. Else we could not commune with Him until we are perfected.......
Wayne Jacobsen’s book, “He Loves Me” (one of the best books ever written on the love of God) addresses this matter much better than I ever could - I highly recommend it.
In your rebuttal, you provided the very reason that Jesus was necessary. Without Jesus, there is no forgiveness of sin. Without Jesus, no sinner could ever enter God’s presence.
You see, a perfect God provides justice. And perfect justice requires atonement or payment for sin. Once a person’s sins are paid, they can be forgiven. That is what Jesus did. He paid the price for our sins, thus our sins CAN be forgiven. They are not automatically forgiven. Forgiveness requires the individual repent and accept Jesus as their Lord and savior. It is a grace that has not been earned nor could ever be earned.
When we stand before God (perfection) on Judgement Day, all of our sins will be covered / paid for by Jesus and we will therefore be sinless before God, who will then welcome us into heaven. In other words, there is no need for perfection (purgatory) as Jesus makes us perfect.
Otherwise, the thief would not have been able to enter paradise “this day”. In effect, belief in the catholic teaching of purgatory calls Jesus a lair because it says that the catholic teaching of purgatory supersedes Jesus’s forgiveness of sins.