This verse is usually interpreted as a prophetic word by Jesus about Himself:
Matthew 12:40: For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.—King James Version
Jesus was crucified and buried on Friday night. On Sunday morning he was discovered by Mary as a resurrected One, which means that only two nights had passed: one from Friday to Saturday, and the other one from Saturday to Sunday.
Can anyone please explain to me, in simple terms, how is it three days and three nights?
A little bit of Friday, Saturday and a little bit of Sunday could be properly describe as three days and nights in Biblical language. We think of days as 24 hour periods but they included in their common expressions a 'day' as 'any part of a day, or 'touching any part of a calendar day'. The term 'three days and three nights' was a Jewish expression that means 'any period that touches three days, including the nights.' Therefore even 26 hours could be three days and nights, if one hour touched a different day on each end.
Some people have been perplexed over this phrase and invent alternate theories on which day what exactly happened around the death of Christ, but I have noticed most who study it deeply seem to revert back to the traditional view that Christ died on a Friday and rose on a Sunday.
However just to be thorough, it must be admitted there is 'some difficulty' in being assured of this answer purely based on the reference to a Hebraism, because it involves trying to trace potentially lost Hebrew meanings two thousand years later. But at a surface level we can at least find very similar instances. For example, a young man fell sick in 1 Samuel 30:12 and he had not eaten any food or drunk any water for ‘three days and three nights’ in the following verse he describes these ‘three days and three nights’ as simply ‘three days’ for he says, ‘I became ill three days ago’. Does three days mean the same thing as three days and night? Since we know that three days could be three periods of time that touch three days when only two nights are within this span, can we infer the phrase ‘three days’ is only different to ‘three days and three nights’ in word but not meaning?
In some way, whether convinced or not, it does not matter to me on two accounts. First, it seems to that early Hebrews and early Christians did not much have difficulty over this phrase. Nobody said, ‘Hey, wait a minute—you rose too early, Jesus.’ I may be wrong but the questioning about when Jesus died and when he rose seems to be a more recent doubt based on ignorance of historical modes of expression. Second, even if it turns out that this Hebraism can only apply to three days and should not extend to three days and three nights, maybe the agony of Christ in the garden is considered by scriptures as the begging of his actual descent into the crucifixion and the 'heart of the earth', not the actual nails being pound into his flesh?
It seems on such trivial matters we need not questions a tradition that Catholics and Protestants have not bothered to question in earlier generations without more to go on. For proof that a Hebrew day was merely a part of a day can be found in this sample article: Three Days and Three NightsTweet