The sad part of the story of the serpent on the staff during the Exodus was that the way to be healed was so simple. The people had only to look and live. Still, many did not. Perhaps they felt it too easy. Perhaps they didn’t believe that Jehovah would truly save them. Alma invokes that experience to bring this people’s choice into clear focus. Alma is presenting them with the way to begin to have faith, with the way to worship, and with the true focal point of that worship. All they need to do is to take that first step.
If they can do so, if they can “plant this word in [their] hearts,” they will know that it is true. Alma is able to promise that, should they do so, “[their] burdens may be light,” because he clearly knew that his father’s people had experienced that very blessing. In the land of Helam they had been heavily burdened, but the Lord made their burdens light, or made them stronger to make the burdens appear lighter. Alma can speak to this from his father’s experience.
This is one of the cases in Mormon’s writing where a testificatory Amen does not end a chapter. It is possible that this Amen does not trigger a chapter ending because Mormon is copying from Alma’s record and Alma didn’t end a chapter at this point. Mormon simply kept working from the text and kept it as Alma had written it.