Sforno on Numbers 6:13/ספורנו על במדבר ו׳:י״ג

1יביא אותו, our sages in B’rachot 8 have already explained this to mean that the Nazirite is to bring himself, as it were. Normally, when someone is being prepared for a higher status than that he had attained in the past, such a person is being “brought” to his new assignment by someone superior to himself. This is why the person afflicted with tzoraat is brought to the Temple. Here. the Nazir presents himself in the Temple instead of being brought, i.e. presented by someone superior. Compare Leviticus 14,2 concerning the צרוע, and concerning the Sotah where the Torah had also written in Numbers 5,15 that the husband was to bring his wife to the priest. Similarly, a Jewish servant, asking to extend his term of service beyond the original 6 years, is brought to the door post to have his ear pierced by his master. (Exodus 21,6). Contrary to all this, the Nazirite at the end of his term who will once more begin to shave the hairs of his face and head, thus becoming “a new man,” brings himself. The reason is simple. There is no one on a higher spiritual niveau who could act as the one “bringing” him, i.e. presenting him.