Further, it appears that the new birth is itself instantaneous. Nothing in the descriptions of the new birth suggests that it is a process rather than a single action. It is nowhere characterized as incomplete. Scripture speaks of believers as “born again” or “having been born again” rather than as “being born again” (John 1:12-13; 2 Cor. 5:17; Eph. 2:1, 5-6; James 1:18; 1 Peter 1:3, 23; 1 John 2:29; 5:1, 4–the relevant Greek verbs in these references are either in the aorist tense, which points to an occurrence without reference to duration, or in the perfect tense, which points to a state of completion). While it may not be possible to determine the precise time of the new birth, and there may be a whole series of antecedents, it appears that the new birth itself is completed in an instant.
Although regeneration is instantaneously complete, it is not an end in itself. As a change of spiritual impulses, regeneration is the beginning of a process of growth that continues throughout one’s lifetime. This process of spiritual maturation is sanctification. Having noted that his readers were formerly dead but are now alive, Paul adds, “For we are God’s workmanship, created in Christ Jesus to do good works, which God prepared in advance for us to do” (Eph. 2:10). He speaks in Philippians 1:6 of continuing and completing what has been begun: “being confident of this, that he who began a good work in you will carry it on to completion until the day of Christ Jesus.” Regeneration is a beginning, but there is much more yet to come. The manifestations of this spiritual ripening are called “fruit of the Spirit.” They are the direct opposite of the fruit of the old nature, the flesh. (Gal. 5:19-23).
Millard Erickson, Christian Theology, p. 957-958