A.T. Robertson Commentary Acts 7:6

"And God spake on this wise, that his seed should sojourn in a strange land, and that they should bring them into bondage, and treat them ill, four hundred years." — Acts 7:6 (ASV)

On this wise (ουτως). A free quotation from Ge 15:13.

Should sojourn (εστα παροικον). Shall be a sojourner, Παροικος (παρα, beside, οικος, home), one dwelling near one's home, but not of it, so a stranger, foreigner, old word, often in LXX, temporary residence without full rights of citizenship (7:29; 13:17), and descriptive of Christians (Ephesians 2:19; 1 Peter 1:17; 1 Peter 2:11).

In a strange land (εν γη αλλοτρια). In a land not one's own, that belongs to another, alien as in Mt 17:25f. , which see.

Four hundred years (ετη τετρακοσια). Accusative of duration of time. As in Ge 15:13, but a round number as in Ex 12:40 the time is 430 years. But in Ga 3:17 Paul, following the LXX in Ex 12:40, takes the 430 years to cover the period in Canaan and the stay in Egypt, cutting the sojourn in Egypt to about half. Josephus gives it both ways. Hackett suggests two solutions, one that there were two ways of reckoning the period among the Jews with no way of settling it, the other that by the 430 years in Egypt the writers meant to include Canaan also as merely the preliminary to the period in Egypt.