Every Old Testament saints did not have the Holy Spirit dwelling in them forming a temple as do Christian believers. (1Cor.3:16)
Some Old Testament saints had the Holy Spirit dwell in them for particular purposes, but not every Old Testament saint had that gift.
If you want to understand dispensational theology, here is a link to an excellent article by Scofield.
http://www.biblebelievers.com/scofield/index.html