Tafsir of Ad-Dhariyat 51:39

(But he turned away with his pillar): He turned away from believing in Moses—peace be upon him. The "pillar" (rukn) refers to the side of his body and his flank; turning with it is a metonymy for turning away. The ba (in bi-ruknih) is for transitiveness, as the meaning is "he bent his flank," or it signifies accompaniment. Qatadah said: "He turned away with his people," based on the view that rukn means "people," as one leans upon them and gains strength through them, with the ba denoting accompaniment or state; its interpretation as denoting causality is not sound. Others said: "He turned away with his power and authority," as rukn is used metaphorically for strength, as stated by al-Raghib. It has also been read as bi-ruknih with a damma on the kaf as a vowel harmony with the ra.

(And said, "A sorcerer"): Meaning, "he is a sorcerer," (or a madman).

The accursed one attributed the extraordinary miracles that appeared at the hands of Moses—peace be upon him—to the jinn, and he wavered between whether they occurred by his choice, in which case it would be sorcery, or without his choice, in which case it would be madness. This was based on his corrupt premise, for otherwise, sorcery does not originate from the jinn, as has been clarified in its proper place. Thus, "or" (aw) is for doubt, though some say it is for ambiguity. Abu Ubaydah said it is in the sense of "and," because the accursed one said both things: "Indeed, this is a learned sorcerer," and, "Indeed, your messenger who has been sent to you is mad." However, you know that the accursed one changes colors like a chameleon, so there is no necessity that compels interpreting it as "and."

(So We seized him and his hosts, and We cast them): We threw them, disregarding them, (into the sea): into the ocean. The intended meaning is that We drowned them therein. The discourse contains an evident indication of the utmost greatness of Divine Power and the final degradation of Pharaoh and his people.