Moshe Ben-Chaim

Question: I have been told that Exodus 13:2 & 24:5 were originally interpreted to mean that the first born son of each Jewish family was intended to be deemed a Cohen to serve as his family's representative to the Holy Temple. I have read the passages and it seems a stretch, is this the way it was before Hashem changed it when only the Levites crossed the line to accept the Torah?
Thank you.

Mesora: Rashi says that when all the Jews sinned by the Golden Calf, except for the Levites, the Levites then replaced the firstborns' designation of Temple service. The firstborns received the priesthood to promulgate Torah ideology, much like the Egyptian firstborns carried the status of passing down their philosophy. We see that the Egyptian firstborns were killed, and as Rabbi once mentioned, it was in order to sever the lineage of those who would teach the corrupt, Egyptian philosophy.
Perhaps it is inherent in the position of first born male, that he commands respect and status. He is then the most fit to act as leader since he carries inherent reverence. Just as killing the Egyptian first born would terminate those leaders, G-d sought Jewish firstborns as natural Torah leaders. However, when they sinned, they were no longer fit to minister to G-d. They showed weakness towards alien G-ds. This contradicts the monotheistic perfection required in Temple worship. Only those perfectly devoted to G-d can relate to G-d in Temple service. Knowledge of His undeniable status as the only G-d is essential for relating to what is truly "Him".