פירוש על קידושין 58:1

R. Yirmiyah limits the dispute in the baraita. If the father really has only five selas, then he redeems himself and not his son. There is only a dispute if the father has five selas that are free and five selas that have a lien over them, meaning he used them to secure a loan or he sold them. According to R. Judah, the “lien” of the Kohen on the five selas owed for the redemption of the father is like a debt written in a document, and therefore it can be collected even from property encumbered with a lien. So the priests would seize five selas worth of land and with this the father would be redeemed. The father can then use the free five selas to redeem himself. But the other rabbis hold that the debt of the five selas cannot be taken from encumbered property. Therefore, he really only has five selas with which he is to redeem himself.