Concise Bible Dictionary:
This term is used in the Old Testament with the force of “to revive, or give new life” in a moral sense: hence we read “quicken me again.” In Psalm 119 the psalmist asked nine times to be quickened—according to God’s word, or His righteousness, or His judgments, &c. (See also Psa. 71:20; Psa. 80:18; Psa. 143:11.) In the New Testament the word is ζωοποιέω, and is invariably employed in the sense of making alive those who are in the state, or under the power of death. It is therefore sometimes used as the equivalent of resurrection, but the word is never applied to the wicked dead. It is God’s work: the term is employed in connection with the Father (John 5:21), with the Son (John 5:21), and with the Spirit (John 6:63). It is characteristic of the last Adam that He is a quickening Spirit (1 Cor. 15:45). In Christ all will be quickened. Evidently the principle of divine sovereignty is involved in the term. God makes alive according to His will. The believer is said to have been quickened together (συζωοποιέω) with Christ, and is thus brought spiritually into association with Christ.
A word may be added on the distinction between “new birth” and “quickening.” It lies in the latter implying a making alive in view of an order of things and a state different from that in which the one quickened had lived previously. This is not necessarily the result of new birth; for instance, Israel will have to be born again in view of earthly blessing (John 3:12; Ezek. 36:25-26); but believers now are not only born again, but, as quickened with Christ, they are made to live spiritually in that sphere of holy love into which Christ has entered by resurrection, in order that He might introduce them into it; they thus have passed from death to life.
From Anstey’s Doctrinal Definitions:
This word means “to be brought to life.” It can be applied to the soul (John 5:21; 6:63; Eph. 2:1, 5; Col. 2:13) and also to the human body (Rom. 4:17; 8:11; 1 Tim. 6:13)—even to the Lord’s body (1 Peter 3:18).
As to the soul, God works upon the elect in sovereign power to bring spiritually dead persons to life by imparting a divine life to them (Eph. 2:1, 5a). As a result, when a person is thus awakened, he is given spiritual faculties whereby he is able to hear and understand spiritual communications from God—i.e. the gospel. Upon believing the gospel and resting in faith on the finished work of Christ, the “quickened” soul is “saved” (Eph. 2:5b, 8). Thus, quickening refers to the same action of the Spirit as being “born again,” but viewed from a different perspective:
New birth views man’s condition as having a corrupted nature, and therefore, in need of a new life and nature, which God imparts by His sovereign power.
Quickening views man’s condition from the perspective of being dead, and thus needing new life from God, which quickening conveys.
Without God sovereignly working in this way in souls, no one would believe the gospel, because prior to quickening, men are spiritually unconscious (being dead), and thus have no capability of hearing and responding to the call of God. (See Born Again and Freewill.)
As to our bodies, Romans 8:11 states that the believer’s body will be quickened, and thus glorified by the Holy Spirit. It does not tell us when this will happen, but we know from other passages that it will be at the Rapture (1 Cor. 15:51-56; Phil. 3:21).