Rather, it is the duty of all to obey. Just because fallen man has no ability to do this does not change the command. That's why every time a lost person rejects the outward call of the gospel he falls deeper and deeper into covenantal curse with God. It's a savor of death unto death.
As we find in Romans 1, the wrath of God is against men for their suppressing the righteousness of God and what is known of Him. All have no excuse in their suppression of the truth of God in unrighteousness.
Even those who have never heard the Good News, including the pagan in the jungle is without excuse for they have a duty to seek after God because of God's general revelation. Paul explicitly says to the pagan Athenians in Acts 17,
Acts 17:26 And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation;
Acts 17:27 That they should seek the Lord, if haply they might feel after him, and find him, though he be not far from every one of us:
Acts 17:28 For in him we live, and move, and have our being; as certain also of your own poets have said, For we are also his offspring.
Accordingly, general revelation reveals enough of God for us to have a duty to seek him, and if we do we will "perhaps reach out for him and find him".
We are to regard repentance and faith as the means by which the great commandment to love God and love our neighbor finds fulfillment. This duty to love God and neighbor existed before the fall and Adam certainly enjoyed the ability to do so. Our love of God is therefore still obligatory, and the means through which it is to be realized, namely repentance and faith, are likewise obligatory. All mankind owe God our love and trust by the very fact that all are His rational creatures. Adam had the ability to love and trust God before the Fall. All are still responsible to love and trust God despite the Fall and while in our unregenerate state, we do not have the ability to do so.
Note here that an imperative (the time is fulfilled, and the kingdom of God is at hand: repent ye, and believe the gospel.) cannot be deduced from an indicative (man has the creaturely power within him to do as he is told). Romanists historically have assumed that the biblical call to perfection implied its possibility. Thanks be to God Luther knew better. What can be and what ought to be are not necessarily coordinate. That all who hear the Good News are under obligation to repent and believe (irrespective of election or reprobation) is not disproved by the reality of the fallen mind. After all, the elect had carnal minds, too, when they first heard the gospel. God's command to believe presupposes man's ability to do so. Firstly, by man's original ability, lost by the fall. Secondly, by a renewed ability, in which the Holy Spirit determines the will of the elect so that they can receive and embrace the gospel offer. [Note: Hyper-Calvinists will deny "duty-faith" on the basis that man now has no ability to believe, but we Reformed reply that the creditor does not lose His right simply because the debtor has lost his estate.]
In summary, fallen man is duty-bound to repent and believe in Christ—even though left to himself he is unable. Biblically speaking, responsibility to God does not imply or necessitate ability on our part. Yet, the basis and motive for the gospel call is not man's duty, but the grace of God in Christ. God everywhere in Scripture commands what man cannot supply, such that we may pray as Augustine, Demand what You will, O Lord, and give what You demand.”
AMR