I have no objection to the concept that some Christians are called from their mothers' wombs (or from the Foundation of the World), and that others have freely chosen to join themselves to Christ in faith (though what does "predestination" mean to a God who created space and time and knows all free-will decisions His creatures will ever make?). However, I see no warrant for arbitrarily assigning the scriptural terms "saints" to one group and "believers" to the other in the New Testament writings as though the saints don't believe and the believers aren't holy.
All saints are believers, not all believers are saints.