Luke 10:1

We have here the sending forth of seventy disciples, two and two, into divers parts of the country, to preach the gospel, and to work miracles in those places which Christ himself designed to visit, to make way for his entertainment. This is not taken notice of by the other evangelists: but the instructions here given them are much the same with those given to the twelve. Observe, I. Their number: they were seventy. As in the choice of twelve apostles Christ had an eye to the twelve patriarchs, the twelve tribes, and the twelve princes of those tribes, so here he seems to have an eye to the seventy elders of Israel. So many went up with Moses and Aaron to the mount, and saw the glory of the God of Israel (Exo 24:1, Exo 24:9), and so many were afterwards chosen to assist Moses in the government, in order to which the Spirit of prophecy came unto them, Num 11:24, Num 11:25. The twelve wells of water and the seventy palm-trees that were at Elim were a figure of the twelve apostles and the seventy disciples, Exo 15:27. They were seventy elders of the Jews that were employed by Ptolemy king of Egypt in turning the Old Testament into Greek, whose translation is thence called the Septuagint. The great sanhedrim consisted of this number. Now, 1.

— Matthew Henry's Concise Commentary (public domain)