What is the meaning of "Nidmeisi"?
Rashi: I will die, for I was not worthy to see the Shechinah. We find that Mano'ach said "Namus Ki Elokim Ra'inu" (Shoftim 13:22). Nidmeisi is like "Nidmah Kol Am Kena'an" (Tzefanyah 1:11).
Radak: Since he heard the great noise, and saw the Bayis fill with smoke, he feared lest he die. He thought that he is not proper to see the honor, rather, to hide his face, like it says "va'Yaster Moshe Panav Ki Yarei me'Habit Elokim ha'Elokim" (Shemos 3:6). This is why he said "Ki Es ha'Melech Hashem Tzevakos Ra'u Einai." "Ha'Melech" is the honor. So Yonason translated. "Nidmeisi" means that I was cut off, like "Nidmah Melech Yisrael" (Hoshe'a 10:15).
Radak citing his father: I became dumb.
Malbim: I was compared in a metaphor
What is "Tamei Sefasaim"?
Rashi: It is repulsive with liabilities.
Radak #1: The first is closed lips, like "Nitminu b'Eineichem" (Iyov 18:3), "v'Nitmesam Bam" (Vayikra 11:43). He considered it a sin for himself that he was not Makdish Kel with the Kochos of the Serafim, for he was not given permission to talk until the angel touched the coal to his mouth.
Radak #2: He mentioned Tum'ah of the lips, and not of the body, because when he heard the Serafim being Makdish Hashem, he told them that for them it is nice to see the honor and be Makdish Hashem, for they are Tehorim, and they can see the honor with their intellect and be Makdish Hashem with their words. However, I am Tamei, for every body of flesh is Tamei, and my lips are Temei'im and not proper to mention Kedushas Kel, when I compare myself to them, and all the more so that I dwell among a nation of Tamei lips! It says about them "v'Chol Peh Dover Nevalah" (9:16). I am not worthy of all this honor! Therefore, I fear lest I die from what I saw. The noise is for me, to eradicate me from the world, for I looked at the honor, and I am Tamei flesh and blood.
Malbim: The moving doorposts was a metaphor that the Navi sinned via his lips, i.e. not rebuking.
Why did he say "I dwell among a nation of Tamei lips"?
Malbim: They do not heed rebuke. The Bayis filling with smoke showed this.
Why did he say "Oy Li"?
Malbim: I and my nation were not worthy of this.
