The Bible divides time into dispensations.
"A dispensation is a period of time during which man is tested in respect of obedience to some specific revelation of the will of God" C. I. Scofield. The test is not to determine his salvation but to show man is a sinner under any rule of life. Salvation is by faith in every dispensation. More on this later.
Every believer is a dispensationalist, whether he believes in two or three or seven dispensations. For instance, every believer knows there is a difference in being under law or under grace.
Then every believer knows there is a difference in being in innocence, as Adam and Eve before the fall, and then under your conscience after the fall when he ate of "the tree of the knowledge of good and evil." Man failed miserably "letting your conscience be your guide" until God sent the flood for "every intent of his heart was only evil continually" Gen. 6:5. Then man was under human government with only Noah and his family, eight in all. They failed miserably without any bad outside influence until God raised up Moses and gave them the Law. Now we live under grace as the rule of life. When the Lord Jesus comes to rule and reign we will be in the thousand year reign of Christ.
Prayer: Father, bless Your dear people and help us to live under grace as a great testimony to a lost world Matt 5:16.