Answer:
"The will to believe" as in like James's previous title "The duty to belief"...
There r virtues in his work ,using this doctrine, adopting beliefs like God, freewill, possibility, and morality would cause evidence to come into existence, thus verifying beliefs that could not have been verified . But it falls apart at the point where he reasons that "morality" {the sense of what is right & what is wrong} stems from the world of men , existing in a Godless , Atheistic , Coincidental universe
For example throughout James' career, he would offer descriptions of what sort of empirical evidence would verify a metaphysical claim. Ultimately, James had never been very concerned with proving the existence of God. His main concern was justifying beliefs in freewill, possibility, pluralism, and in particular, in the possibility of morality.
A useful deduction we {as people who have faith in God can deduce} is that evidently "morality" is not created by "man" .It is instigated by God , our sense of right & wrong.
For example , the science of humanitarianism is all equalling & non discriminatory , to the point where same sex couples can legally cohabitate together , now if we pursued such an nimiety of openness and non discrimination by valuing that which is nothing more than sexual orientation , logically the next step would be to legalise paedophiles ! For in the Godless , Atheistic , world from where Jame's lecture stems from , there would be no obligation in stopping a , say for example , a 54 year old man from marrying & having sex with a 9 year old girl or boy , as a paedophile the 54 year old man would simply state that he is a law abiding citizen , that he pays his taxes , that this 9 year old & him have fallen in love and that this should be legally accepted by the law of the land.
From that we can deduce , that "morality" in the control of "man" could easily go awry , because in reasoning that there is no God, we fail to partake of a divine wisdom , that tempers our evolution in a civil intellectual society , creating this fabric of "morality".
Yes there is need to promote an all equalling society that is non discriminatory , but we must be careful , and in that prudence not cease our yearning for a better world but pray for guidance from that superior being that created the world.
Please remember that "science" {including such works as Jame's} is not against God , but the respective institutes that claim a monopoly on God , and there archaic peculiar customs , traditions , & superstitions