John MacArthur refers to soteriology—the doctrine of salvation—as “the pinnacle of Christian theology” [citation John MacArthur and Richard Mayhue, eds., Biblical Doctrine: A Systematic Summary of Biblical Truth (Wheaton, IL: Crossway, 2017), 485.] That’s understandable considering that our eternal destiny hinges on the correctness of our soteriology.
Throughout this series we’ve examined the simple yet stellar theology of the thief—his right view of God, his right view of himself, his right fear of judgment, and his right recognition of Christ as the one true Savior. And that doctrinal excellence also extends to his right understanding of salvation.
In fact, there is no clearer picture in Scripture of salvation coming to someone by grace through faith apart from works.
“We indeed are suffering justly, for we are receiving what we deserve for our deeds; but this man has done nothing wrong.” And he was saying, “Jesus, remember me when You come in Your kingdom!” And He said to him, “Truly I say to you, today you shall be with Me in Paradise.” (Luke 23:41–43, emphasis added)
The thief knew better than anyone that he had absolutely nothingmeritorious to offer Christ. He had already confessed the justice of the punishment he was enduring. He saw no inherent goodness in himself. And even if he believed in a system of works-righteousness, he had no life left to live to accumulate merit. All he could do was appeal to the Savior in faith. And Jesus responded in grace, pouring out unmerited favor toward the wicked criminal at His side. What could be more gracious than granting a hell-bound wretch full citizenship in God’s heavenly kingdom?
In his hymn “Rock of Ages,” Augustus Toplady echoed the desperate plea of the repentant thief.
Nothing in my hand I bring,
Simply to the cross I cling;
Naked, come to thee for dress;
Helpless, look to thee for grace;
Foul, I to the fountain fly;
Wash me, Savior, or I die.
The thief embodied the glorious soteriological truths we find in Ephesians 2:8–9: “For by grace you have been saved through faith; and that not of yourselves, it is the gift of God; not as a result of works, so that no one may boast.”
Furthermore, the thief’s faith was a repentant faith. There is good reason why the thief who turned to Christ is widely known as the “repentant thief” or “penitent thief.” Verses 40 and 41 clearly reveal a man who acknowledged and despised his guilt. He was a man who willingly confessed his sin, just as all believers are urged to do (1 John 1:9).
Obviously, the thief never had the chance to physically demonstrate his repentance by living a changed life. But we know that a changed life is the result—not the cause—of a changed heart (Ezekiel 36:25–27). And that transformed heart was plainly evident as the thief abandoned the blasphemy he had earlier participated in (Matthew 27:44) and pled with Jesus for mercy.
Christ’s response is both staggering and thrilling for all who come to Him in genuine repentance and faith. As John MacArthur explains,
The Lord’s reply was astonishing. He prefaced it with the word “truly,” because what He was about to say was hard to believe. That a cursed criminal, whom the Jews would view as unredeemable, would be promised entrance to God’s kingdom was an outrageous affront to their sensibilities.
The promise that this redeemed sinner would be with Jesus in heaven that very day invalidates the Roman Catholic teaching regarding purgatory. It also eliminates any system of works-righteousness, since the penitent thief had neither the time nor the opportunity to perform enough good deeds to merit salvation.
The wonderful promise that he would be with Jesus in “Paradise” (heaven; 2 Corinthians 12:2; cf. Revelation 2:7; Revelation 22:2, 14) speaks of his full reconciliation to God. He would not merely see Jesus from afar, he would be with Him. His restoration would be full and complete. 
The grace of God should shock us because God would be perfectly good and just to consign everyone to eternal damnation at any moment. We shouldn’t marvel at His wrath, but His grace should astound us.
Additionally, the sudden transformation of the thief is also shocking. Why did someone so debauched suddenly come to his spiritual senses? It is because God graciously and sovereignly regenerates people who were once dead in sin (Ephesians 2:1) and makes them a new and living creature (2 Corinthians 5:17).
He had initially joined the others in reviling and blaspheming Christ. But then God opened his heart to the truth and miraculously, powerfully, sovereignly, instantly granted him faith and eternal life. The people, the rulers, the Romans, even his fellow thief did not understand what was truly happening at Calvary, but this man suddenly perceived the truth clearly. Through the power of the Holy Spirit, he was rescued from spiritual darkness and death and given light and life. Like Paul on the road to Damascus, he perceived the truth through a divine miracle in his soul. 
When we consider the superb theology of the thief, we must remember that it was initially imparted to him by God. And that’s true of all good theology. Those who truly know God came to that knowledge through an act of His saving grace.
And that brings us back to where we began this series, with revered and celebrated theologians who can’t enunciate the fundamentals of the Christian faith with clarity and simplicity. People who spend their lives exploring theological obscurities often end up obfuscating or ignoring the vital truths the thief understood and clearly communicated. Through their corrupting and confusing of the gospel, they invalidate their spiritual credentials and prove the uselessness of academic clout apart from a redeemed heart. And when such scholars are wrong about the fundamentals of the gospel, they might as well be wrong about everything else.
For those reasons, the theology of the thief provides the basic building blocks for all good theology. May God grant us the grace to understand His truth with similar accuracy and precision.
Source: Cameron Beuttel | Grace to You