“Paul’s buildup to this point [in Romans 1:16-17] enables him to introduce it [the gospel] with great force in a bold and confident affirmation. He is not ashamed or afraid to confess the gospel even in face of the distinctions made in v. 14, even though the gospel as to its origin or content, or he himself, might be classified as barbarian and lacking in wisdom (cf. 1 Cor. 1-2). The reason for his confidence is not because he can dispute such an inference, nor because of the gospel’s sophistication or appeal to the rational mind, but because it is the power of God to salvation. That is to say, his confidence in the gospel rests in what is for him a clear and simple fact: the gospel is the effective means by which God brings about the wholeness and preservation of the whole person. He does nto say when this goal will be achieved, and there is certainly no implication that it will be instantaneous; his confidence is simply that the goal will be achieved. This is a point worth grasping even at this early stage: Paul does not see the gospel as something which merely begins someone on the way to salvation, but as something which embraces the totality of the process toward and into salvation. The gospel is not merely the intitial proclamation of Christ which wins converts, but is the whole Christian message and claim–in terms of the rest of the letter, not just chaps. 1-5, or 1-8, or even 1-11, but the whole letter.
This observation bears also on the next phrase–‘to all who believe’–for it follows from what has just been said that Paul here is talking not just about the initial acceptance of the proclamation of the crucified and risen Christ, but about that together with the life which follows from it as the whole process which leads into final wholeness. This is the point of the present tense–‘to all who believe and go on believing’; namely, to all who not only come to a decision of faith, but whose whole life is characterized as a trustful acceptance of and committment to the gospel which is God’s power to salvation.” (James D. G. Dunn, Romans 1-8, WBC, pp. 46-47)