My response to Gerstner's statement is that he obviously does not understand what Dispensationalists teach. For example, C. I. Scofield's New Scofield Reference Bible (p. vii) states "As a further aid to comprehending the divine economy of the ages, a recognition of the dispensations is of highest value, so long as it is clearly understood that throughout all the Scriptures, there is only one basis for salvation." Charles Ryrie, author of Dispensationalism, has a whole chapter addressing the false claim that Dispensationalism teaches more than one way of salvation.
"Jesus saith unto him, I am THE WAY, the truth, and the life: NO MAN COMETH UNTO THE FATHER BUT BY ME" (Jn. 14:6). And yet, there were many Gentiles and Jews who never heard of Jesus, and yet, they are viewed as righteous by God. The first chapter of the Book of Hebrews declares that the Creator of the Universe, Jesus (v. 1-2), paid for the sins of mankind (v. 3). In the eleventh chapter, the writer lists the "heroes of the faith"; that is, those who, BELIEVING AND TRUSTING IN GOD, demonstrated their faith by their actions.
In addition, Abraham, a Gentile chosen by God to be the father of the Nation of Israel, is declared to be righteous three times in the New Testament. Romans 4:3 says, "For what saith the Scripture? Abraham believed God, and it was counted unto him for righteousness." Galatians 3:6 says, "Even as Abraham believed God, and it was accounted to him for righteousness." And finally, James 2:23 says, "And the Scripture was fulfilled which saith, Abraham believed God, and it was imputed unto him for righteousness: and he was called the Friend of God."
It was his failure to believe God that caused the fall of Adam in the first place, and through him, the fall of all mankind (Gen. 3:1-6; 1 Cor. 15:22; etc.). Throughout Scripture, the use of the word, "believe" when it comes to saving faith, is always present tense. Those who are "saved" believe in God. Those of us who have been born again by faith in Jesus Christ, remain saved because it is God's work in us that brings us into Christ-likeness (Phil. 1:6; 1 Jn. 3:2).
The Bible gradually reveals God's truth (Heb. 1:1-2).
Those who believe the light they have are saved - period!