Study Sukkah folio 20A with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
And this is what the Mishnah is saying: With regard to a large mat of reeds, if one produced it for the purpose of lying upon it, it is susceptible to ritual impurity, and one may not roof a sukka with it. The reason is that one produced it specifically for the purpose of lying upon it; however,
Abaye said to him: If so, if their dispute is only with regard to a small mat, then instead of saying: R' Eliezer says: Both a small mat and a large mat, the Mishnah needed to say: Both a large mat and a small mat. In a phrase with the format: Both this and that, one typically mentions the more obv
And furthermore, there is proof that when they disagree, it is with regard to a large mat, and R' Eliezer’s opinion is a stringency and not a leniency, as it is taught in a baraita: In the case of a reed mat, with a large mat one may roof a sukka. R' Eliezer says: If it is not susceptible to ritua
Rather, Rav Pappa said: Rava’s proposed resolution is rejected. Rather, with regard to a small mat, everyone agrees that if it was produced without designation, presumably it is for the purpose of lying upon it. When they disagree, is with regard to a large mat: The first tanna holds that a large
What, then, is the meaning of: If one produced it for the purpose of lying upon it, that R' Eliezer states? This is what he is saying: Making mats without designation is also for the purpose of lying upon it, until one makes it specifically for roofing.