Why does it say "Mi Kel
Radak: This is unlike those who trust in their idols. Since I always overcome them, they should know that their molten images are false, and there is no Rock like ours.
Radak citing Targum Yonasan: At the time of Mashi'ach, all the nations will admit that there is none like Hashem.
Radak (Tehilim 18:32): Who can annul His word and what He commanded?!
Why does it switch from Kel to Hashem?
Malbim (Tehilim 18:32): Shem Havayah alludes to the Creation; He was Mehaveh (brought into existence) everything found. Shem Kel alludes to conduct and Hashgachah. Elokim, who conducts and supervises according to deeds, He Himself is Hashem who created the entire Creation and established the laws of nature. There is no power that creates and forms other than Elokeinu, who conducts and supervises. The conductor is the Creator, and the Creator is the conductor. Surely He arranged that there is no contradiction between the laws of nature and the laws of conduct. The former are drawn to conform to the latter.
Why does it say "u'Mi Tzur
Radak (Tehilim 18:32): Who can turn back His decree?!