Then went up Moses, and Aaron, Nadab, and Abihu, and seventy of the elders of Israel:
Then went up Moses, and Aaron ... - in obedience to a command given (Exodus 24:1-2; also Exodus 19:24) previous to the religious engagement of the people, described above.
Nadab, and Abihu - the two oldest sons of Aaron, whose approach to God on this occasion was preparatory to their consecration to the priestly office.
And seventy of the elders - a select number. What was the principle of selection is not said; but they were the chief representatives, the most conspicuous for official rank and station, as well as for their probity and weight of character in their respective tribes.