The 600,000 were males above 20 years of age, Num 1:3-43. This would make the entire body not less than 2,000,000 of people of all ages. Succoth was the first rallying point on which the various bands converged. It stood in open country, over which their flocks and herds spread themselves. It was, indeed, a night to be observed, when the Exodus took place, because, as Bunsen says, it was the beginning of history; and we may almost say further that it was the hour when Israel was born as a nation. God called His son out of Egypt. At that moment also the period of which Abraham had been apprised ran out. See Gen 15:13; Gal 3:17; and Exo 12:40 here.
Notice the stress laid on circumcision, which was the type of putting away the sins of the flesh. See Col 2:11. We must be separated from sin, before we can claim our portion in the Paschal Lamb, or join the Exodus.