As Christ is the omega point of redemptive history, Adam is its alpha point.
Image bearers of Adam is hardly an apt, much less valid or even intelligible, description of human beings who are held either to have existed before Adam or subsequently not to have descended from him.
Believers with bear Christ's "heavenly" image , the redeemed and glorified image of God, as they have borne Adam's "earthly" image, the original image of God defaced by sin. It is quite foreign to this passage, especially given its comprehensive outlook noted above, to suppose that some not in the image of Adam will bear the glory-image of Christ. There is no hope of salvation for sinners who do not bear the image of Adam by ordinary generation. Christ cannot and does not redeem what he has not assumed, and what he has assumed is the nature of those who bear the image of Adam and as they do so by natural descent.
Without the "first" the Adam is, there is no place for Christ as either "second" or "last".
For Paul, redemptive history has its clear and consummative ending with Christ only as it has a definitive and identifiable beginning with Adam.
"John 7:24. Judge not according to the appearance." ... Circumcision was properly held by them in reverence; and when it was performed on the Sabbath-day, they knew that the Law was not violated by it, because the works of God agree well with each other. Why do they not arrive at the same conclusion as to the work of Christ, but because their minds are preoccupied by a prejudice which they have formed against his person? Judgment, therefore, will never be right, unless it be regulated by the truth of the fact; for as soon as persons appear in public, they turn their eyes and senses on them, so that the truth immediately vanishes. While this admonition ought to be observed in all causes and affairs, it is peculiarly necessary when the question relates to the heavenly doctrine; for there is nothing to which we are more prone than to dislike that doctrine on account of the hatred or contempt of men.
A sinner is not always aware of the time when he crossed from death to life. What initially seemed to be preparation may later prove to have been salvation. The regenerating work of the Spirit is a mystery; we must acknowledge that the wind blows where it pleases and we do not see it (John 3:8).
The question... is whether we may speak of the Abrahamic covenant (singular, so the Reformed) or Abrahamic covenants (plural, so the Baptists). The antipaedobaptists had to speak of two covenants made with Abraham: works and grace. By doing so, they were able to argue that circumcision belonged to the Abrahamic covenant of works and not to the Abrahamic covenant of grace.
Reformed theologians typically included the covenant made with David in their works on the history of redemption because of the abundant revelations made to David. These revelations include Christ’s eternal sonship; His threefold office of prophet, priest, and king; His incarnation, His mediatorial sufferings, and death; His resurrection, ascension into heaven, and enthronement at God’s right hand; the rise, progress, and success of His church and kingdom in the earth; His appointment to judge the world at the last day; and His eternal glory, in which all who belong to Him are destined to share.
Thus the covenant of grace was made unilaterally by God; it is called a “one-sided covenant” (foedus monopleuron), given to fallen sinners apart from any consideration of their natural ability to respond or to fulfill the terms of the covenant. However, the covenant of grace is conditional in that it requires faith in Christ on man’s part, and so may be also called a “two-sided covenant” (foedus dipleuron).5