Matthew 12:39-40

The evil and adulterous generation was the larger group of unbelieving Jews that the scribes and Pharisees represented. Adultery is a common Old Testament metaphor for spiritual apostasy, departure from God (Isaiah 50:1; Isaiah 57:3; Jeremiah 3:8; Jeremiah 13:27; Jeremiah 31:32; Ezekiel 16:15; Ezekiel 16:32; Ezekiel 16:35-42; Hosea 2:1-7; Hosea 3:1; Hosea 7:13-16). God had granted signs in the past to strengthen the weak faith of believers such as Abraham, Joshua, and Gideon. Jesus refused to give His critics one since they wanted a sign to trap Him rather than to bolster weak faith.

The sign of Jonah was not a sign for the scribes and Pharisees. It became a sign to believers in Him later. The sign of Jonah means the sign that Jonah was to the Ninevites. He signified one whom God had delivered from certain death. [Note: Eugene H. Merrill, "The Sign of Jonah," Journal of the Evangelical Theological Society 23 (1980):23-30.] Jesus’ use of "Son of Man" stressed His suffering role (cf. Matthew 8:20). The "heart" of the earth may recall Jonah 2:3 (cf. Psalms 46:2). This is a reference to Jesus’ burial. Jesus was saying that His deliverance from death in the grave, which would be similar to Jonah’s deliverance, only greater, would prove His claims. As the Jews reckoned time, three days and three nights meant three full days or any parts of three days. [Note: Carson, "Matthew," p. 296.] Jesus was in the grave for parts of three days.