John Calvin Commentary 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 their uncircumcision: three years shall they be as uncircumcised unto you; it shall not be eaten." — Leviticus 19:23 (ASV)

And when you shall come. There seems to me no question that the circumcision of trees, as well as of men, pertains to the First Commandment: not only that the Jews might see a symbol of their own adoption in the very trees, but also that they might learn that only the children of God were permitted to feed on their fruit; and also that whatever the earth produces is, in a way, profane until it is purified.

For surely by this ceremony was shown what Paul teaches: that all things are sanctified by the word of God and prayer (1 Timothy 4:5); this is not because anything is in itself impure, but because the earth has contracted pollution from humanity's corruption, it is just, regarding us, that the harmless fruits also should be regarded as uncircumcised.

In sum, God would raise up a wall by which He might separate His people from the Gentiles, and at the same time admonish them that a legitimate use of what the earth produced could not be made by the sons of Adam, except by special privilege.

But the analogy of uncircumcision, until the year appointed for the trees to be circumcised, was a very appropriate one, so that they might acknowledge the fruits of their trees to be pure for them by the same right by which they themselves were consecrated as God’s peculiar people.

But, so that the three years’ unproductiveness would not press too heavily upon them, He promises them compensation from the future blessing of God; for if they abstained from eating the unclean fruit, a larger produce was to be expected in the future.