Soteriology is the study of salvation
"The traditional orthodox or evangelical position on salvation is correlated closely with the orthodox understanding of the human predicament. In this understanding, the relationship between the human being and God is the primary one. When that is not right, the other dimensions of life are adversely affected as well.37
Evangelicals understand the Scriptures to indicate that there are two major aspects to the human problem of sin. First, sin is a broken relationship with God. The human has failed to fulfill divine expectations, whether by transgressing limitations that God’s law has set or by failing to do what is positively commanded there. Deviation from the law results in a state of guilt or liability to punishment. Second, the very nature of the person is spoiled as a result of deviation from the law. Now there is an inclination toward evil, a propensity for sin. There is a bias, as it were, away from the good, so that the person tends by nature to do evil. Usually termed corruption, this often shows itself in terms of internal disorientation and conflict as well. Beyond that, because we live in the context of a network of interpersonal relationships, the rupture in our relationship with God also results in a disturbance of our relationships with other persons. Sin even takes on collective dimensions: the whole structure of society inflicts hardships and wrongs upon individuals and minority groups.
Certain aspects of the doctrine of salvation relate to the matter of one’s standing with God. The individual’s legal status must be changed from guilty to not guilty. This is a matter of one’s being declared just or righteous in God’s sight, of being viewed as fully meeting the divine requirements. The theological term here is justification. One is justified by being brought into a legal union with Christ. More is necessary, however, than merely remission of guilt, because the warm intimacy that should characterize one’s relationship with God has been lost. This problem is rectified by adoption, in which one is restored to favor with God and enabled to claim all the benefits provided by the loving Father.
In addition to the need to reestablish one’s relationship with God, there is also a need to alter the condition of one’s heart. The basic change in the direction of one’s life from an inclination toward sin to a positive desire to live righteously is termed regeneration or, literally, new birth. An actual alteration of one’s character is involved, an infusion of a positive spiritual energy. This, however, is merely the beginning of the spiritual life. The individual’s spiritual condition is progressively altered; one actually becomes holier. This progressive subjective change is referred to as sanctification (“making holy”). Sanctification finally comes to completion in the life beyond death, when the spiritual nature of the believer will be perfected. This is termed glorification. The individual’s maintaining faith and commitment to the very end through the grace of God is perseverance.
As we have done with respect to other issues, we will adopt the evangelical position on salvation. Although God is concerned about every human need, both individual and collective, Jesus made clear that the eternal spiritual welfare of the individual is infinitely more important than the supplying of temporal needs. Note, for example, his advice in Matthew 5:29–30: “If your right eye causes you to sin, gouge it out and throw it away. It is better for you to lose one part of your body than for your whole body to be thrown into hell. And if your right hand causes you to sin, cut it off and throw it away. It is better for you to lose one part of your body than for your whole body to go into hell.” His rhetorical question in Mark 8:36 makes the same point: “What good is it for a man to gain the whole world, yet forfeit his soul?” God’s preoccupation with humans’ eternal spiritual welfare and the biblical picture of sin are compelling evidence for the evangelical view of salvation. We saw in chapter 28 that sin originates in the individual human through personal voluntary choice in response to temptation. And we observed in chapter 30 the radical and thoroughgoing nature of human sin. This “total depravity,” as it is termed, means that a radical and supernatural transformation of human nature is necessary for forgiveness and restoration to favor with God."
Erickson, M. J. (1998). Christian theology. (2nd ed., pp. 917–919). Grand Rapids, MI: Baker Book House.
Union With Christ
"The Scriptures declare that, through the operation of God, there is constituted a union of the soul with Christ different in kind from God’s natural and providential concursus with all spirits, as well as from all unions of mere association or sympathy, moral likeness, or moral influence,—a union of life, in which the human spirit, while then most truly possessing its own individuality and personal distinctness, is interpenetrated and energized by the Spirit of Christ, is made inscrutably but indissolubly one with him, and so becomes a member and partaker of that regenerated, believing, and justified humanity of which he is the head.
Union with Christ is not union with a system of doctrine, nor with external religious influences, nor with an organized church, nor with an ideal man,—but rather, with a personal, risen, living, omnipresent Lord (J. W. A. Stewart). Dr. J. W. Alexander well calls this doctrine of the Union of the Believer with Christ “the central truth of all theology and of all religion.” Yet it receives little of formal recognition, either in dogmatic treatises or in common religious experience. Quenstedt, 886–912, has devoted a section to it; A. A. Hodge gives to it a chapter, in his Outlines of Theology, 369 sq., to which we are indebted for valuable suggestions; H. B. Smith treats of it, not however as a separate topic, but under the head of Justification (System, 531–539).
The majority of printed systems of doctrine, however, contain no chapter or section on Union with Christ, and the majority of Christians much more frequently think of Christ as a Savior outside of them, than as a Savior who dwells within. This comparative neglect of the doctrine is doubtless a reaction from the exaggerations of a false mysticism. But there is great need of rescuing the doctrine from neglect. For this we rely wholly upon Scripture. Doctrines which reason can neither discover nor prove need large support from the Bible. It is a mark of divine wisdom that the doctrine of the Trinity, for example, is so inwoven with the whole fabric of the New Testament, that the rejection of the former is the virtual rejection of the latter. The doctrine of Union with Christ, in like manner, is taught so variously and abundantly, that to deny it is to deny inspiration itself. See Kahnis, Luth. Dogmatik, 3:447–450."
Strong, A. H. (1907). Systematic theology (p. 795). Philadelphia: American Baptist Publication Society.