The Source and Meaning of Upsherin

The custom's deepest root lies in the laws of orlah: Vayikra 19:23-25 states that the fruit of a newly planted tree is forbidden for three years and may not be eaten, and Nitei Gavriel, Upsherin 1 concludes, on our reading of the cited page, that children are initiated into the parallel negative commandment of not rounding the corners of the head (pe'os), so that the first haircut is treated as an educational milestone tied to that prohibition — making Vayikra 19:23-25 the starting point for understanding the custom.

A second layer of meaning is supplied by Rabbeinu Bahya (Bamidbar 6:3), who teaches that a person's hair is bound up with their inner strength — as the verse about Shimshon illustrates — and that the commandment to let hair grow points to something spiritually significant about hair's connection to divine vitality, so that deliberately managing when and how it is first cut carries religious weight beyond the merely practical.