38 But if ye neglect the tree, and take no thought for its nourishment, behold it will not get any root; and when the heat of the sun cometh and scorcheth it, because it hath no root it withers away, and ye pluck it up and cast it out.
39 Now, this is not because the seed was not good, neither is it because the fruit thereof would not be desirable; but it is because your ground is barren, and ye will not nourish the tree, therefore ye cannot have the fruit thereof.
We often think of this chapter as an application of the scientific method to spiritual knowledge. There is an important difference, however, between a purely scientific inquiry and the experiment which Alma recommends to us here. Science attempts to be objective: the researcher is an observer, not a participant, and when he or she interacts with the object of study, it is only to see how it will react, not to insert themselves into the environment. The scientist always remains impartial and independent.
But there is no way to exclude ourselves from the experiment which Alma describes. You cannot objectify spiritual knowledge. Just as forced humility is of limited value, so also spiritual knowledge which comes from outside of us (“Show me a sign!”) fails to accomplish its purpose (v. 16-18).
And so, if this experiment fails, it may be a false negative result: the word may be true (we may even have seen evidence of it earlier in the experiment–see v. 30), but we may not experience the expected growth because we are unwilling to fully engage in the exercise. If we fail to nourish the plant, it will not grow; the environment in which the plant must grow is us.