One of the malefactors - Matthew Mat 27:44 says "the thieves - cast the same in his teeth." See the apparent contradiction in these statements reconciled in the notes at that place.

If thou be Christ - If thou art the Messiah; if thou art what thou dost pretend to be. This is a taunt or reproach of the same kind as that of the priests in Luke 23:35.

Save thyself and us - Save our lives. Deliver us from the cross. This man did not seek for salvation truly; he asked not to be delivered from his sins; if he had, Jesus would also have heard him. Men often, in sickness and affliction, call upon God. They are earnest in prayer. They ask of God to save them, but it is only to save them from "temporal" death. It is not to be saved from their sins, and the consequence is, that when God "does" raise them up, they forget their promises, and live as they did before, as this robber "would" have done if Jesus had heard his prayer and delivered him from the cross.

One of the malefactors which were hanged - It is likely that the two robbers were not nailed to their crosses, but only tied to them by cords, and thus they are represented in ancient paintings. If not nailed, they could not have suffered much, and therefore they were found still alive when the soldiers came to give the coup de grace, which put a speedy end to their lives. John 19:31-33.

And one of the malefactors, which were hanged,.... On the cross, one of the thieves crucified with Christ; the Oriental versions add, "with him"; according to the Evangelists Matthew and Mark, both of them reviled him, and threw the same things in his teeth as the priests, people, and soldiers did; which how it may be reconciled; see Gill on Matthew 27:44.

railed on him, saying, if thou be Christ, save thyself, and us; taking up the words of the rulers, and adding to them, perhaps, with a design to curry favour with them, hoping thereby to get a release; or, however, showing the wickedness and malice of his heart, which his sufferings and punishment, he now endured, could make no alteration in; see Revelation 16:9.

Railed (ἐβλασφήμει)

Imperfect: kept up a railing.

{g} And {12} one of the malefactors which were hanged railed on him, saying, If thou be Christ, save thyself and us.

(g) Therefore we must either take Matthew's account to be using the figure of speech synecdoche, or that both of them mocked Christ. But one of them who was eventually overcome with the great patience of God breaks forth in that confession worthy all memory.

(12) Christ, in the midst of the humbling of himself upon the cross, indeed shows that he has both the power of life to save the believers and the power of death to avenge the rebellious.

23:39 One of the malefactors. Matthew and Mark represent the malefactors as mocking him (Mt 27:44 Mr 15:32). It may be that only one spoke, apparently for both, or that both spoke at first, and then one was silent.

If thou be the Christ. Art not thou the Christ ? (Revised Version). That Jesus did not save himself and his companions in suffering seemed to this malefactor to prove that this was not the Christ.

23:39 And one of the malefactors reviled him - St. Matthew says, the robbers: St. Mark, they that were crucified with him, reviled him. Either therefore St. Matthew and Mark put the plural for the singular (as the best authors sometimes do) or both reviled him at the first, till one of them felt the overwhelming power of saving grace.

Lu 23:39-43. The Two Thieves.

39. railed on him-catching up the universal derision, but with a turn of his own. Jesus, "reviled, reviles not again"; but another voice from the cross shall nobly wipe out this dishonor and turn it to the unspeakable glory of the dying Redeemer.

23:32-43 As soon as Christ was fastened to the cross, he prayed for those who crucified him. The great thing he died to purchase and procure for us, is the forgiveness of sin. This he prays for. Jesus was crucified between two thieves; in them were shown the different effects the cross of Christ would have upon the children of men in the preaching the gospel. One malefactor was hardened to the last. No troubles of themselves will change a wicked heart. The other was softened at the last: he was snatched as a brand out of the burning, and made a monument of Divine mercy. This gives no encouragement to any to put off repentance to their death-beds, or to hope that they shall then find mercy. It is certain that true repentance is never too late; but it is as certain that late repentance is seldom true. None can be sure they shall have time to repent at death, but every man may be sure he cannot have the advantages this penitent thief had. We shall see the case to be singular, if we observe the uncommon effects of God's grace upon this man. He reproved the other for railing on Christ. He owned that he deserved what was done to him. He believed Jesus to have suffered wrongfully. Observe his faith in this prayer. Christ was in the depth of disgrace, suffering as a deceiver, and not delivered by his Father. He made this profession before the wonders were displayed which put honour on Christ's sufferings, and startled the centurion. He believed in a life to come, and desired to be happy in that life; not like the other thief, to be only saved from the cross. Observe his humility in this prayer. All his request is, Lord, remember me; quite referring it to Jesus in what way to remember him. Thus he was humbled in true repentance, and he brought forth all the fruits for repentance his circumstances would admit. Christ upon the cross, is gracious like Christ upon the throne. Though he was in the greatest struggle and agony, yet he had pity for a poor penitent. By this act of grace we are to understand that Jesus Christ died to open the kingdom of heaven to all penitent, obedient believers. It is a single instance in Scripture; it should teach us to despair of none, and that none should despair of themselves; but lest it should be abused, it is contrasted with the awful state of the other thief, who died hardened in unbelief, though a crucified Saviour was so near him. Be sure that in general men die as they live.