Many of todays presentations are of the no commitment type. And we all know that we are save by grace through faith and not of works. I agree it is the Holy Spirit's job to show a person that a commitment is needed. Lets suppose that it is never mentioned as part of the Gospel presentation. This fact is sure, if a person has not repented, the person has not been converted.
Lets examine some bible references, and see if a committement is required.
It would seem that a commitment is not required, only believe. But that would over simplify what the word believe means. The word believe in the bible means to commit. To just give a mental assent to some facts is not what the word believe means. In our society believe is used very loosely.