I have a question that I've heard several explanations for in the past. Speaking of his death, burial and resurrection, Jesus said in Matthew 12:40: For as Jonah was three days and three nights in the belly of a huge fish, so the Son of Man will be three days and three nights in the heart of the earth. Friday through Sunday morning doesn't work out to 3 days and 3 nights.
This question has vexed non-Jewish people in every generation, for the Scripture is clear that the literal time frame in which Jesus was in the tomb was two nights, two days, and part of a third day. The Jewish people of the day, however, did not question this well-known saying of Jesus (Matt. 27:63), even though they might easily have used it to charge Jesus as being a false prophet because he wasn’t in the tomb for 72 hours before His resurrection.
The reason this charge was never made is that the Jews understood this saying as accurate. Why? Because it was a long accepted practice of the Jewish people in calculating time to treat part of a day as a whole day. There are many examples of this in Scripture as well as in non-biblical sources.
For example, 2 Chronicles 5:7 & 12 tells us: Rehoboam answered, “Come back to me in three days.” So the people went away. Three days later Jeroboam and all the people returned to Rehoboam, as the king had said, “Come back to me in three days.” We do not know what time of day or night they arrived, nor does it matter. They could not afford to be as precise in setting appointments as we have grown accustomed to. If you showed up any time during the 24 hour period, you were on time. Any part of the day or night was considered a day.
“Three days and three nights” in Matthew 12:40 was a common figure of speech in the Jewish culture of Jesus’ day. Because we typically get side-tracked on the precise measurement of time, we also end up missing the point of the “sign of Jonah” Jesus’ intended. The meaning of the sign was to compare Jesus’ miraculous resurrection with Jonah’s miraculous deliverance from the huge fish’s belly. We don’t know what portion of those days and nights Jonah actually spent in suffocating stomach acids. What we do know is that what should have been certain death became a demonstration of the power of God.
To the roots of the mountains I sank down; the earth beneath barred me in forever. But you brought my life up from the pit, O LORD my God (Jonah 2:6).
As with Jonah, so also the Son of Man was not allowed to be defeated by death: …because you will not abandon me to the grave, nor will you let your Holy One see decay (Acts 2:27). This was the sign of Jonah.