In Matthew 12:40, Jesus says that He will spend three days and three nights in the grave, as Jonah spent three days and three nights in the belly of the great fish. But if Jesus was crucified on Friday and rose on Sunday, He rose on the third day, but He only spent two nights in the grave. On the other hand, if we extend His stay in the tomb to include three nights, He would wind up rising on the fourth day.
The answer is that the phrase ‘three days and three nights’ is an idiom that does not require there to be three nights.
Jonah was swallowed by the fish during the day time and was vomited out during the day time (Jonah 1:17—2:10). In order for that to be three days, only two nights could have been involved. Yet it is called three days and three nights. Similarly, in Esther 4:16—5:1, there is a fast for ‘three days and three nights’ that begins on the first day and ends on the third day, which means only two nights were involved. So we must conclude that this is an idiom that observes that each of the days had a night associated with it.
Now let’s go to the theater and sit in the same row. I’ll sit in Seat One next to the aisle, and you sit in Seat Three. I am sitting in the first seat, and you are sitting in the third seat, which is two seats away from me, and there is one seat between us. Call the seats ‘Friday,’ ‘Saturday,’ and ‘Sunday.’ Now it is clear: Jesus was buried on Friday, He rose on Sunday, which is the third day.
Jesus was in the grave three days and three nights in the same sense that Jonah was in the belly of the great fish three days and three nights. Remember John 21:25: Scripture contains everything we need for our salvation, not everything we need to satisfy our curiosity. It is written so that we might have faith in Jesus Christ, not check up on Him.
In the ancient church, everyone everywhere always accepted that Jesus was crucified on Friday and rose on Sunday, and that it constituted ‘three days and three nights.’
For more details, read about Holy Week.