This is an always an cantankerous subject among Christian theology and its students; the role between the objectivity of salvation accomplished by God in Jesus Christ, and the existential appropriation of that and inclusion in that (or not) by the human agent. Karl Barth offers the best way forward on this impasse (that will just not pass via classical and traditional attempts), by grounding both the objectivity and existential reality of salvation—surprise!—in the vicarious humanity of Christ. With an emphasis on the universal scope of salvation, in Christ, Barth provides a better grounding (in a theological-anthropology and a Triune-shaped doctrine of God) for accessing this variegated conundrum that just won’t seem to let go for many a Christian thinker. But I think we ought to let this go, and rest in the vicarious humanity of Christ; and rest in the dialectic kind of tension that is present if and only if we follow a God who is dialogically present, and dynamically given, in the resurrection of Jesus Christ. Here is how George Hunsinger comments on this in the theology of Karl Barth:
The history of every human being is seen as included in that of Jesus. The history of Jesus is taken as the center which establishes, unifies, and incorporates a differentiated whole in which the history of each human being as such is included. This act of universal inclusion is his accomplishment and achievement. He enacts our salvation as a gift which is valid and efficacious for all. The validity and efficacy of this gift cannot be denied without compromising (among other things) the absolutely unconditioned and therefore gratuitous character of divine grace in him. This denial would therefore be unjustifiable within the web of Christian (or biblically derived) beliefs. The inclusion of every human being’s history in that of Jesus is therefore described according to the pattern of dialectical inclusion. No one is excluded from the validity and efficacy of what took place for our salvation in Jesus Christ. In his history is objectively included the history of each and all.
Conversely, the history of Jesus is viewed as included in that of every human being. Although this history and what it accomplishes occur in definite sequence in time and a definite location of place, they are not encapsulated in that time and place in an unqualified way. On the contrary, they are present, in a mysterious and differentiated way, and in ways known and as yet unknown, to the history of each and every human being as such. Just as their history is enclosed in his, so is his enclosed in theirs, with all its efficacy and validity. The continual, miraculous, and mysterious presence of his history (and therefore he himself to theirs (and therefore to themselves) cannot be denied without denying (among other things) his resurrection from the dead. Therefore his denial, too, would be unjustifiable within the web of Christian beliefs. The inclusion of Jesus’ history in that of everyone else’s is therefore described according to the pattern of actualism. The once-for-all event of Jesus’ history, without ceasing to such, reiterates itself so as to be present to the history of and each and every human being. In the history of each and all, his history is objectively included. [George Hunsinger, How To Read Karl Barth: The Shape of His Theology, 110-11. Nook]
Barth eludes the usual approach to this theological conundrum; indeed the point of entrance (a faulty presumption about the elect and reprobate) that leads to this as a theological conundrum. By seeing grace as the reality that predicates and grounds humanity, the humanity of God for us in Christ, it is impossible to deny its universal and ontological reality; if we do—as Barth would contend—then we would have to deny the mystery of God become human. It is not possible then to dissect creation, and humanity as its crown, into a sufficient and efficient mass; as if God’s grace in salvation is sufficient for all of creation, but only efficient for the particularly elect. If grace funds all of creation (as Romans 8:18ff requires), then it does. Barth allows the dialectic of Scripture to be truly dialectical in this regard; which then invites continued dialogical engagement with our Triune God. Barth’s theology of creation and grace does not shut down inquiry, but opens it up toward and from our Triune God who is full of mercy and grace.