Tafsir of Ya seen 36:16

"They said, 'Our Lord knows that we are indeed messengers to you.'"

They (the messengers) called upon the knowledge of Allah the Exalted as a witness. This serves the same function as an oath in terms of emphasis and in the manner of responding to what requires a response. It has been mentioned that whoever invokes the knowledge of Allah falsely commits disbelief (kufr), which is not the case for swearing a false oath. In this, there is a warning to them against opposing the knowledge of Allah the Exalted. In the selection of the title of Lordship (Rububiyah), there is an allusion to the wisdom behind the sending [of messengers], just as the disbelievers alluded to what contradicts it in their claim.

Attributing 'Lord' to the pronoun of the messengers does not conflict with this. It is possible that it was chosen because it is more appropriate to the state in which they find themselves—that of the manifestation of miracles at their hands. It is as if they said, "Our Supporter through miracles knows that we are indeed messengers to you." The placing of the predicate before the subject ("Our Lord knows") is for the strengthening of the judgment or for restriction (hasr), meaning: "Our Lord knows [the truth], not you," due to your lack of consideration of the signs.