Whenever we attempt to gather the meaning of a passage in Scripture, we must compare it with other similar or related passages. This allows the Bible—the inspired Word—to interpret itself. Since the term “heart of the earth” is found only in Matthew 12, and nowhere else in Scripture, we need to find similar verses to reference.
The phrase “in the earth” appears 66 times in the King James Bible, but none of these refers to the grave. For instance, in the Lord’s Prayer we pray, “Thy will be done in earth as it is in heaven.” Does this mean we’re praying for God’s will to be done in the tomb as it is in heaven? No, of course not. Rather, it means His will among the people of earth—the nations of the earth—as it is done among the angels in heaven.
In the second commandment, we read, “Thou shalt not make unto thee any graven image, or any likeness of any thing that is in heaven above, or that is in the earth beneath, or that is in the water under the earth” (Exodus 20:4). We easily recognize here that “in the earth beneath” does not mean in the grave, but rather in the world. Jesus also says, “Blessed are the meek: for they shall inherit the earth” (Matthew 5:5). Does that mean they will inherit the tomb?
I think you get my point.
In Matthew 12:40, the word “heart” comes from the Greek word kardia, which is where we get the word “cardiac.” According to Strong’s, kardia means the heart (i.e., thoughts or feelings [mind]); it also can mean the middle. Additionally, the Greek word for “earth” is ge. It literally means soil, a region, or the solid part or whole of the terrene globe (including the occupants in each application)—including country, ground, land, or world.
So the phrase “in the heart of the earth” can easily be translated as “in the midst of the world”--or in the grip of this lost planet—-that Jesus came to save!
In other words, in Matthew 12:40, the Lord is telling His disciples that just as Jonah was in the belly of a great fish, so the Son of Man would be in the central clutches of the world.
So in the context of 3 days and 3 nights in the grip of this liost planet... In the heart of the the corrupt kingdoms and under their control... Thursday night was when Jesus was arrested and came under the power and authority... Willingly of course... Of Satan's earthly kingdom.