Commento su Esodo 13:11

והיה כי יביאך AND IT SHALL COME TO PASS WHEN [THE LORD] SHALL BRING THEE … [THOU SHALT SET APART etc.] — There are some of our Rabbis who learned from this statement that the firstborn who were born in the wilderness were not thus hallowed. He who says that these were thus hallowed explains this “coming” (i. e. this verse, which appears to make the hallowing of the firstborn dependent upon their arrival in the land) as follows: if you observe it (this command) in the wilderness, you will be privileged to enter the land and to observe it there (cf. Bekhorot 4b).

AND IT SHALL BE WHEN THE ETERNAL SHALL BRING THEE INTO THE LAND OF THE CANAANITES. This is stated because the law of that which “openeth the womb” [mentioned in Verse 12], applied only from the time they came to the Land of Israel.³⁹¹See my Hebrew commentary p. 344 for correctness of this reading as based on Ramban manuscript. It is also borne out by Ramban’s statement further on in this section: “But the commandment… did not apply to the firstborn in the wilderness.”
In line with the plain meaning of Scripture, the verse, Sanctify unto Me all the firstborn, [mentioned in Verse 2 above] means all the firstborn living at that time. Since He redeemed them from death when He smote in the land of Egypt, He commanded [in that verse above] that they be sanctified to Him to do the work of G-d, whatever He will command them to do. He did not command them at this time concerning the redemption of the firstborn, but only after He exchanged them for the Levites and He commanded the redemption of the firstborn that were over and above the number of the Levites.³⁹²Numbers 3:44-47. But the commandment [as expressed in the verse, Sanctify unto Me all the firstborn], did not apply to the firstborn in the wilderness. Now, [in the verse before us], He commanded that when they shall come into the Land of Israel, the law should apply to the firstborn of both man and beast³⁹³Verse 12. and the firstling of an ass,³⁹⁴Verse 13. and then He commanded the law of their redemption for the generations.³⁹⁴Verse 13.

והיה כי יביאך, "It will be when He will bring you, etc." The Torah underlines once more that it is G'd who will bring you to the Holy Land so that you should not forget about His commandments in the belief that you yourself have achieved all this, especially after your border will gradually extend further and further. Although this commandment is not applicable until after conquest of the land, it remains in force even if the land is lost as it is a commandment that involves the body and not the earth. Kidushin 36 teaches that all commandments which are performed by one's body apply throughout the ages and wherever a Jew resides.