Tafsir of Ash-Shu`ara' 26:55

"And indeed, they are to us [a source of] rage"

They are doing that which enrages us by defying our command and departing without our permission, along with what they possess of our borrowed wealth; for it has been narrated that Allah, the Exalted, commanded them to borrow ornaments from the Copts, so they borrowed them and departed with them.

The placement of "to us" (lana) before the predicate is for the purpose of restriction and to suit the rhyming cadence. The particle lam is for strengthening the meaning, or it is a case of treating a transitive verb as though it were intransitive.