Jacob places this experience in dialogue. It is part of the stylistic inheritance from the Old World that important lessons are couched in dialogue. The interchange allows the principles to be taught in a more gradual and interesting way, as opposed to straight exposition.
Sherem gets right to the point. Jacob has taught the doctrine of Christ, and Sherem declares that this is a perversion. In particular, he contrasts the doctrine of Christ with the law of Moses, which he declares “is the right way.” The issue is that the doctrine of Christ is wholly reliant upon an atoning Messiah who will not come for over half a millennium.
Sherem denies that any being so far distant could be important now, and that Jacob could not know that his coming would be important because “no man knowest of such things; for he cannot tell of things to come.” While this appears to be a condemnation of prophecy, it should not be read so broadly. The Old Testament supported prophets, and as one who declared that the law of Moses was the right way, Sherem would have to accept prophets, including the principle of prophecy. It is not any prophecy, but rather this particular one.
In the Book of Mormon, the atoning Messiah is often referred to as one who would come, or even that which is to come. All that Sherem says, and does, declares that his particular issue is the teaching of the atoning Messiah and not prophecy in general.