Anthony Hoekema, in his book Saved by Grace, gives a good summary of the effects that one's view of the effectual call of the gospel had in relation to one's view of the nature of man.
The 'gospel call' is the demand the gospel places on all men everywhere to repent and believe the gospel. The 'effectual call' is that which results on one man's responding to the gospel call while another does not.
According to Hoekema, one's view of the nature of man has great impact on whether one sees a distinction between the gospel call and effectual call at all, and the relation between them and the nature of man.
The Pelagian View
Man is morally and spiritually neutral so that he is free to choose to do good or bad. No effectual call is necessary.
The Semi-Pelagian View
Man is morally and spiritually sick, but all still have the ability to respond to the gospel. No effectual call is necessary.
The Arminian View
Man is depraved, but there is sufficient enabling grace such that those who hear the gospel can cooperate with this grace and accept the gospel. No effectual call is necessary.
The Reformed View
Man is dead in sin, unable on his own to respond favorably to the gospel call. Effectual calling is necessary to bring the man to life and enable him to respond.
It is certainly apt to suggest that the doctrines of grace all fall into place once the biblical picture of the nature of man is accepted. As J.I. Packer said, one needs only be a one-point Calvinist: God Saves Sinners.