The Thief's Appeal

 The one thief on the cross must have concluded that Jesus was the Christ, and that he could appeal to his mercy. This account is similar to the parable of the Pharisee and the tax collector.

I've done some rethinking of the thief's request and faith when he asked Jesus to “remember” him:

³⁹ Then one of the criminals who were hanged blasphemed Him, saying, "If You are the Christ, save Yourself and us." ⁴⁰ But the other, answering, rebuked him, saying, "Do you not even fear God, seeing you are under the same condemnation? ⁴¹ And we indeed justly, for we receive the due reward of our deeds; but this Man has done nothing wrong." ⁴² Then he said to Jesus, "Lord, remember me when You come into Your kingdom." ⁴³ And Jesus said to him, "Assuredly, I say to you, today you will be with Me in Paradise." Luke 23:39-43

The one thief makes reference to Jesus being “the Christ,” which would suggest they (the 2 thieves) knew this claim being made of Jesus. The one thief was saying it with ridicule, but the other thief, probably having a change of mind (cp. Matthew 27.44), rebuked the one who made ridicule, having come to a fear of God in their hopeless state.

The thief who had a change of mind recognizes the innocence of Jesus and the just consequences of their situation. And instead of ridiculing the claim that Jesus was the Christ, he must have accepted that claim. And in acceptance of that claim, knowing that the Christ was both Son of God and king of Israel, the thief appealed to his mercy.

The Old Testament says that God desires mercy over sacrifice. Jesus said: ³ But go and learn what this means: I desire 'mercy and not sacrifice.' For I did not come to call the righteous, but sinners, to repentance." Matthew 9:13 (⁶ For I desire mercy and not sacrifice, And the knowledge of God more than burnt offerings. Hosea 6:6)

This appeal by the thief came from an acceptance in who Jesus was, being the Christ, and he made the appeal for mercy as he acknowledged his sins and trusting that Jesus could grant it.

This is similar to the parable by Jesus about the Pharisee and the tax-collector:

⁹ Also He spoke this parable to some who trusted in themselves that they were righteous, and despised others: ¹⁰ "Two men went up to the temple to pray, one a Pharisee and the other a tax collector. ¹¹ The Pharisee stood and prayed thus with himself, 'God, I thank You that I am not like other men—extortioners, unjust, adulterers, or even as this tax collector. ¹² I fast twice a week; I give tithes of all that I possess.' ¹³ And the tax collector, standing afar off, would not so much as raise his eyes to heaven, but beat his breast, saying, 'God, be merciful to me a sinner!' ¹⁴ I tell you, this man went down to his house justified rather than the other; for everyone who exalts himself will be humbled, and he who humbles himself will be exalted." Luke 18:9-14

The tax collector, in the parable, acknowledged his sinfulness and appealed to the mercy of God. The pharisee trusted in himself, that he was righteous, comparing himself to the tax collector. Jesus said the tax collector went to his house justified rather than the pharisee.

There's definitely a similarity between the thief on the cross and the tax collector, because both make an appeal to Divine mercy.

We know from Divine revelation that the death of Christ was for sins. It is because of this Divine sacrifice for sins (the “propitiation”) that God is just in justifying us through faith:

²¹ But now the righteousness of God apart from the law is revealed, being witnessed by the Law and the Prophets, ²² even the righteousness of God, through faith in Jesus Christ, to all and on all who believe. For there is no difference; ²³ for all have sinned and fall short of the glory of God, ²⁴ being justified freely by His grace through the redemption that is in Christ Jesus, ²⁵ whom God set forth as a propitiation by His blood, through faith, to demonstrate His righteousness, because in His forbearance God had passed over the sins that were previously committed, ²⁶ to demonstrate at the present time His righteousness, that He might be just and the justifier of the one who has faith in Jesus. Romans 3:21-26

Some may argue the mercy of God was accomplish at the cross, while others would say it is in saving us from our sins (forgiveness of sins or justification) or from our sinful nature (regeneration or eternal life).

In the account of the thief and the parable of the tax collector, you have individuals who made an appeal to divine mercy. Whether they could understand the divine basis of that mercy or not, they trusted the one who could grant it.

Unlike the thief who still had a mind of ridicule towards Jesus and the self-righteous pharisee, these acknowledged their sinfulness and need, and they believed/ trusted in and appealed to the mercy that only God can give. Therefore, the thief was given assurance of being in Paradise, and the tax collector was said to be justified.