Albert Barnes Commentary Psalms 66:9

"Who holdeth our soul in life, And suffereth not our feet to be moved." — Psalms 66:9 (ASV)

Which holdeth our soul in life—The margin, as in Hebrew, reads “puts.” That is, He has put (or placed) us in a state of safety. The word rendered “in life” literally means “among the living.” The word “soul” here is equivalent to us—ourselves; and the idea is that He keeps us among the living. What is said here of this special deliverance is true of all people at all times: they owe the fact that they are among the living to the care of God; or, it is because He puts them among the living, or keeps them alive.

And suffereth not our feet to be moved—That is, from their firm position of safety. The idea is taken from one who is walking and who is kept from slipping or falling.