What is the parsing of the "Lām" in "latacūdunna" in verse 13 of Sūrat Ibrāhīm?

The lam in the Almighty's saying: (or you return to our religion) is the lam of oath, and (you return) is conjoined by (or) to the implied answer of the oath (we will surely expel you). The disbelievers swore that the messengers would either be expelled from the land or return to their religion, as if they said: "By Allah, we will surely expel you from our land, or you will return to our religion." The exegetes explained that "return" here means "to become," because the messengers were never upon their religion at all.