12:39 seeketh after a sign. “Sign” is the same word as “miracle.” This rebuke from Christ seems applicable to those Christians today who are continually looking for miraculous manifestations of one kind or another. We already have the completed Word of God, with abundant testimony to its inerrant authority, not to mention the tremendous scientific evidence of creation and historical evidence of Christ’s victory over death, so there is no need for further miraculous confirmation of our faith.
12:40 whale’s belly. The remarkable miracle of Jonah and the great fish (Jonah 1:17) has been ridiculed by many generations of skeptics, but the Lord Jesus confirmed that it really happened. Furthermore, He appropriated it as a prophetic type of His own coming death and resurrection. The Greek word translated “whale,” incidentally, does not necessarily mean “whale,” but any great marine animal.
12:40 three days and three nights. If “three days and three nights” is taken to mean literally seventy-two hours, there would be an apparent contradiction with the many prophecies and records that He would rise on “the third day” (Matthew 16:21; 20:19; John 2:19; I Corinthians 15:4; etc.), This reckoning would oppose the uniform tradition of the church that He was crucified on Friday and rose on Sunday. The problem is resolved if one assumes that any portion of a day or night could be idiomatically reckoned as a “day and night.” Actual extra-Biblical justification for assuming this idiomatic usage here exists. Thus, if three calendar dates are involved, they can be counted as the entire three days and nights. At least two similar usages can be found in the Old Testament. Note Esther 4:16 in comparison with Esther 5:1, and also I Samuel 30:12 with I Samuel 30:13.
12:41 The men of Nineveh. The unique revival in the wicked city of Nineveh at the preaching of Jonah is here verified by the Lord Jesus.