I Just realized this!
The Arminian conception of gospel preaching is weak, because it depends on the preacher's personal ability and strength. - Therefore: People must hear to believe, so that must be contingent upon the preachers personality, ability, strength, voice tone, eloquence etc. - That obviously can not be the case!
The Calvinist, on the other hand, knows that God's Word will never fail to accomplish all that God desires it to accomplish.
"So will My Word be which goes forth from My mouth; it will not return to Me empty, without accomplishing what I desire, and without succeeding in the matter for which I sent it." Is. 55:11