I came across this excerpt from Rav Saadia Gaon on reincarnation (on mesora.org, where they cite it as Saadia Gaon: “The Book of Beliefs and Opinions” “Refutation of Reincarnation” Yale Judaica Series, Vol. I “The Soul” chap. VIII pp 259") and I'm having trouble understanding part of what he's saying. For context, in the excerpt, Rav Saadia Gaon strongly objects to those who consider reincarnation to be an authentic part of Judaism. In it, he identifies one of the arguments made by proponents of belief in reincarnation as being that the suffering of small children is inconceivable given the idea that God is just, unless their soul had sinned in a previous life. (Setting aside how that could actually work, for the purposes of this question.)
Within the excerpt, Rav Saadia Gaon refutes this in two ways, with the first refutation being that people get compensated in the afterlife for suffering in this world. (Again, setting aside whether that would actually make the suffering itself morally justified, for the purposes of this question.) So I understand that part. But then, it's Rav Saadia Gaon's second refutation I'm having trouble making sense of:
Furthermore we should like to ask [proponents of belief in reincarnation] what they conceive the original status of the soul to be – we mean its status when it is first created. Is it charged by its Master with any obligation to obey Him or not? If they allege that it is not so charged, then there can be no punishments for it either, since it was not charged with any obligations to begin with. If, on the other hand, they acknowledge the imposition of such a charge, in which case obedience and disobedience did not apply before, they thereby admit that God charges His servants with obligations on account of the future and not at all on account of the past. But then they return to our theory and are forced to give up their insistence on the view that man’s suffering in this world is due solely to his conduct in a previous existence.
What is Rav Saadia Gaon getting at with statements about whether a soul initially is charged with obligations, and what is his subsequent reasoning on that? Is he simply suggesting that people are punished for their future crimes? And if so, why bother with that suggestion at all when it wouldn't cover all circumstances (in particular, small children who suffer and do not survive long enough to sin), when his earlier suggestion (that compensation in the afterlife makes it justifiable to cause children to suffer) would apply to more circumstances?
My best attempt at understanding what he said is that the only way a soul could be subject to punishment for sins is if at one point an obligation is imposed on the soul for the future, and if an obligation can be made now for future actions, then God interacts with the soul at one point based on something in the future, so we should just say that it can also be punished at one point based on future actions. Is that what he's saying, did I miss part of the reasoning, or am I totally off the mark?