Ramban on Exodus 28:1/רמב"ן על שמות כ״ח:א׳

1AND THOU BRING THOU NEAR AARON THY BROTHER, AND HIS SONS WITH HIM … THAT THEY MINISTER UNTO ME IN THE PRIEST’S OFFICE, EVEN AARON, NADAB AND ABIHU, ELEAZAR AND ITHAMAR, AARON’S SONS. The reason for mentioning Nadab and Abihu, Eleazar and Ithamar [when it mentioned already “and his sons”] is that Moses should not think that by anointing the father to minister as priest, his sons would automatically become priests; instead he had to initiate them personally into the priesthood. Thus Phinehas [the son of Eleazar] and others already born were excluded [from the priesthood], for only these four sons who were anointed with Aaron, and their children born to them henceforth, were appointed as priests.