Dispensationalism is defined by one reliable scholar in Bible matters as: “A period of time during which man is tested in respect to his obedience to some specific revelation of the will of God” (New Scofield Reference Bible on Gen. 1:28).
Old Testament believers have their specific requirements from their specific revelation from God, and we in the Church Age have ours. The requirements, and the revelation upon which those requirements are based, are not identical in every dispensation.
Dispensations can be discerned by considering that different eras were under different covenants given by God.
The Adamic Covenant
The Noahic covenant
The Abrahamic Covenant
The Mosaic Covenant
The New Covenant, or Covenant of Grace
All dispensations require belief in God’s way to Redemption. The Old Testament saints looked forward to the Messiah -God’s sacrificial grace gift to redeem mankind. Saints today look back to that sacrifice by the Lord Jesus Christ, who fulfilled God’s redemptive requirements