Until the horrific events of Jesus’ crucifixion had taken place and His disciples understood there was no way mortal life could be restored to His body—but then, there He was, alive and well, and could be handled, and could eat and drink with them—until then they couldn’t understand the many words He had spoken to them concerning His death and resurrection. He had told them, repeatedly, that it would happen. But even after the tomb was found empty, and He had appeared to Mary Magdalene, and Peter, and the two on the road to Emmaus, they still couldn’t believe it. Such is the power of death as an impenetrable veil of darkness that the devil had used since the Fall to enslave men to their fears, which armor Christ plundered by His death and resurrection to set them free. Now, having the experiential knowledge of hindsight, He could open their minds to understand from the Scripture what before had been so opaque. Luke summarizes His eye-opening revelation to them in three words that encapsulated the gospel imperative to which they were now witnesses: that the Christ was to suffer, and to rise again on the third day, and that repentance for forgiveness for sins was to be heralded in His name to all nations, beginning in Jerusalem. That the Messiah would not only die but suffer was necessary to the central purpose of His mission to save men from their sins (Mat 1:21). For deliverance from the power of sin comes only through death, and it is he who has suffered in the flesh who has ceased from sin; see Rom 8:13, 1Pe 4:1-2.
In spite of a number of pieces of the prophetic puzzle that alluded to the Lord’s suffering servant, which in hindsight became clear in identifying Jesus as the Messiah, until it actually happened the full picture of how those pieces fit together remained obscure. Much less was there an understanding of the resurrection from the dead to immortal life (as something distinct from those like Lazarus who had been raised from the dead to mortal life); cf. Mar 9:9-10, Joh 20:9 and note that in both of these passages rise from the dead or rise again translates the Greek word ἀνίστημι which is the root form of the word for resurrection (ἀνάστασις), as distinct from the word ἐγείρω that was typically used for raising from the dead to mortal life, i.e., a resuscitation, which prior to Christ’s resurrection was the only raising from the dead people could comprehend. Although there are a few allusions to the resurrection in texts that the Sadducees didn’t accept as authoritative (Job, Psalms, and Daniel), those allusions and the greater argument for the resurrection that Jesus pointed out to them come only from a devout faith in God’s promises, that there must be a resurrection or God could hardly be called the God of Abraham, Isaac and Jacob, who died in faith that God is a rewarder of those who seek Him, but without having received the promises.
Notice though even more from what Jesus opened their minds to understand, not only that the nebulous hope of the resurrection was a reality, of which He was now living proof, but that the Scriptures had foretold that He as the Messiah, after suffering, would rise again or be resurrected from the dead (Greek ἀνίστημι) on the third day (Luk 24:46) to positively identify Him. From where does it become clear in hindsight not only that the Messiah would be resurrected, but that it would happen on the third day? See Psa 16:9-10 (cf. Act 2:27-31, 13:34-37), Lev 23:10-11 (cf. 1Co 15:20,23, Col 1:18 and note God’s perfect timing of the Passover that year that allowed for the Christ to be crucified on Thursday as the religious leaders were sacrificing their Passover lambs, laid in the tomb that evening, and then raised from the dead as the first fruits from the dead on the third day following: Friday being the first day, Saturday the second day, and Sunday—the day after the Sabbath in terms of Lev 23:11—the third day). See also Hos 6:1-2. Recall too the sign of Jonah that Jesus gave on multiple occasions that pointed toward His resurrection after being three days and three nights in the heart of the earth; see Jon 1:17, 2:1-2,6, Mat 12:39-40, 16:4, Luk 11:29-30. Finally, also observe that the word for arise or rise again that bespoke the resurrection (ἀνίστημι), occurs in much greater proportion to the number of verses in the book of Jonah than in any other book of the TaNaK; see Jon 1:2,3,6, 3:2,3 as well as Jon 3:6 where a cognate Greek and the same Hebrew word behind the other 5 occurrences also occurs.
In what way do these six verses above from Jonah that highlight God’s concern for the Gentiles of Nineveh also bespeak the third word with which Luke summarizes Christ’s mission, to herald repentance for the forgiveness of sins to all the nations? Where else in the TaNaK did it speak of the Messiah’s mission extending past the nation of Israel to all the nations, i.e., to the Gentiles (as the word is even more commonly translated)? See Gen 12:3, Psa 2:6-8, 22:23,27, 67:1-7, 86:9, 98:2-3, Isa 2:2-4, 11:10, 49:6,22, 52:10,15, 60:1-3, 66:18-19, Hos 2:23, Mal 1:11. What example do we have of Jesus’ followers heralding not only the gospel of Christ’s suffering and resurrection, but repentance for the forgiveness of sins to all nations, starting in Jerusalem? See Act 2:23-24,38, 3:18-19,22,25-26, 5:30-32, 11:18, 13:27-35,38-39,46-47, 17:3,30-31, 20:21, 26:20,22-23, Rom 1:16.