Jesus' statement in Luke 23:43 is not so much about the afterlife or what's required of us to get into heaven. It's primary purpose is to depict Jesus' death as undoing the curse of Adam.
Luke presents Jesus as a new Adam.
This is beyond a doubt the purpose in Luke's placement and arrangement of Jesus’ genealogy. Unlike Matthew who places his genealogy at the outset of his gospel, Luke places it immedietly after Jesus’ adult baptism and just prior to the temptations. It’s thus bookended by the issue of Jesus’ sonship. In the baptism God declares Jesus to be His “beloved Son” and in the temptations Satan challenges Jesus, ”if you are the Son of God…”
When all the people were being baptized, Jesus was baptized too. And
as he was praying, heaven was opened and the Holy Spirit descended
on him in bodily form like a dove. And a voice came from heaven: “You
are my Son, whom I love; with you I am well pleased.” (Luke 3:21-22)
Luke then records the genealogy and then...
Jesus, full of the Holy Spirit, left the Jordan and was led by the
Spirit into the wilderness, where for forty days he was tempted[a] by
the devil. He ate nothing during those days, and at the end of them he
was hungry. The devil said to him, “If you are the Son of God, tell
this stone to become bread.” (Luke 4:1-3)
Also instead of beginning with Abraham and working forward to Jesus, as Matthew does (Matthew 1:1-16), Luke genealogy begins with Jesus and works backwards to Adam (Luke 3:23-38). The net effect makes this genealogy a list of sons rather than a list of fathers and points to Adam rather than Jesus.
Matthew is a list of fathers starting with Abraham.
Abraham was the father of Isaac, Isaac the father of Jacob, Jacob the
father of Judah and his brothers, 3 Judah the father of Perez and
Zerah, whose mother was Tamar, Perez the father of Hezron, Hezron the
father of Ram...
Luke is a list of sons ending with Adam and God.
the son of Methuselah, the son of Enoch, the son of Jared, the son of
Mahalaleel, the son of Cainan, 38 the son of Enosh, the son of Seth,
the son of Adam, the son of God.
Of course Luke’s intention is not to diminish Jesus but rather to make a comparison between Jesus and Adam. Both Jesus and Adam are said to be God’s son.
Luke presents Jesus as tempted like Adam.
Jesus’ three temptation follow immediately after the genealogy. If Luke intends to present Jesus like Adam than the temptations could not have been better placed. But Jesus’ success here is merely the beginning of a battle that will continue in the later part of Luke. Luke tells us that after the temptations the devil, ”left him until an “opportune time” (4:13). In Luke, Satan finds this opportunity at the beginning of the crucifixion plot, entering into Judas Iscariot (Luke 22:3).
This suggests that the events surrounding the crucifixion are themselves a continuation of the temptation. Certainly there are echoes of the devil’s challenge at the trial when the leaders ask, “Are you the Son of God…” (22:70). And it’s Jesus’ bold “Yes!” which seals his fate, overcoming the potential desire to save his own skin.
As with the other gospels Jesus confession is juxtaposed with Peter’s denial. If Peter’s denial is due to, as Luke tells us, the sifting of Satan (22:31-32) then there is little doubt Satan is also present in this challenging question to Jesus. It echoes the devil’s challenge in the earlier temptations.
Luke presents Jesus undoing the curse of Adam.
At Jesus’ death, the centurion declares, “surely this man was innocent!” Here Luke differs remarkably from the centurion’s confession in the gospels of Matthew and Mark. In those accounts the centurion says, “Truly this man was the Son of God!” Owing to the fact that Luke has already declared Jesus to be the Son of God, it is doubtful that Luke wants to downplay this fact here. Instead it appears the verdict of innocence is in some sense connected to Jesus being like Adam, the Son of God.
For Luke, Jesus’ innocence is not simply in reference to the crime for which He has been charged but instead refers to his victory over all temptation. What Christ has done in his persistent innocence is to reopen the way closed by Adam. Jesus final words to the thief on the cross are directly connected to this second Adam motif, “Truly, I say to you, today you will be with me in Paradise.” “Paradise” is the same Greek word used elsewhere in Septuagint and the book of Revelation for the “garden” of Eden.