Leviticus 19:23
And when ye shall come into the land, and shall have planted all manner of trees for food, then ye shall count the fruit thereof as uncircumcised: three years shall it be as uncircumcised unto you: it shall not be eaten of. And when ye shall come into the land, and shall have planted all manner of trees for food, then ye shall count the fruit thereof as uncircumcised: three years shall it be as uncircumcised unto you: it shall not be eaten of.
The command was spoken less than a year after the departure from Egypt while Israel was still at Sinai, and was not a law first given forty years later in Deuteronomy. When food trees are planted in the land, their fruit is to be counted as uncircumcised for the first three years of bearing and is not to be eaten. The chapter belongs to laws God gave Israel that stand in clear contrast to the customs of the nations around them.
The laws governing Israel in this passage are ethical rather than ceremonial. Treating the early fruit as set apart and unfit for use impressed that worship and service to God are holy, just as the sinful nations in the land were destroyed for their wickedness. The nations cast out of the land before Israel had given themselves to pagan abominations with Satan ruling through the flesh, and after four hundred years of mercy in which God sent His servants to sojourn among them to win them to the right way they filled up their cup of iniquity, so their blotting from the earth was a blessing to future generations.