Question

I would appreciate the Rabbi’s help in understanding Rabbi Elchanan’s words here (section 132) regarding the presumption of fitness for a doubtful son of a divorced woman, on account of his father, who had the established status of a fit priest:
 And it must be said that the law of the father is that his son should be like him; and if we disqualify the son, that is a change in the father’s legal status, and we therefore maintain the father in his presumption, that his status has not changed.
[The explanation I tried to suggest (maybe a bit forced): it is as though there are two halakhic worlds, the son’s world and the father’s world. The question whether the son is fit or disqualified also exists in the father’s world, because the father’s fitness requires a basic fitness of the sons (“Grandpa was a priest, Dad was a priest, I also want to be a priest”..), unless some external factor intervened (such as marriage to a captive woman or a definitely divorced woman). According to Tosafot, this basic fitness turns the son into an extension of the father’s fitness and part of his halakhic world, and in the father’s world the presumption of fitness is operative, preventing a doubt about external intervention (= possible divorced woman or captive woman) from changing the son’s halakhic status.]