John Gill Commentary Psalms 135:12

"And gave their land for a heritage, A heritage unto Israel his people." — Psalms 135:12 (ASV)

And gave their land [for] an heritage
The land of the two kings before mentioned, which was given to the Reubenites, and Gadites, and half tribe of Manasseh, (Deuteronomy 3:12–17) ; and the lands belonging to the several kingdoms of Canaan were given to the rest of the tribes;

an heritage unto Israel his people ;
a type of the heavenly Canaan, the glorious, incorruptible, undefiled, and eternal inheritance; which is of God's free grace, chosen, prepared, and given; even a right unto it, and meetness for it, to the true and spiritual Israel of God, to his special people, his chosen, redeemed, and called ones.