Albert Barnes Commentary Psalms 105:12

"When they were but a few men in number, Yea, very few, and sojourners in it." — Psalms 105:12 (ASV)

When they were but a few men in number - literally, "As they were a countable people, very few." That is, they could then be easily numbered, and they were so few that they could not take possession of it themselves. This is in contrast with the promise then made to them that they should be in number as the stars, and as the sand on the seashore.

And strangers in it - Foreigners. They were mere sojourners. They did not become incorporated with the people of the land. They did not acquire property there. They were regarded and treated as belonging to a foreign people. See the notes at Hebrews 11:9.