Tafsir of Ya seen 36:7

(The word has come to pass) is the response to an omitted oath; meaning: "By Allah, it has been established and rendered inevitable." (The word) refers to that which I said to Iblis on the day he said: "I will surely mislead them all," and which is: "I will surely fill Hell with jinn and mankind all together."

(Upon most of them) is attached to "has come to pass." The intended meaning is that it has preceded in My knowledge that most of them will be among those with whom I fill Hell; they are the followers of Iblis, as indicated by the precedence of "jinn" over "mankind" [in the cited verse], and as explicitly stated by His saying: "I will surely fill Hell with you and with those who follow you among them, all together."

There is no barrier to interpreting "the word" as meaning "decree," though the aforementioned interpretation is the most famous. The apparent speech of al-Raghib suggests that what is meant by "the word" is the knowledge of Allah Almighty regarding them, but there is no need to commit to that. It is also said that the prepositional phrase is attached to "the word," and it is said, "He spoke against him" when one speaks of him with evil; the intended meaning is "My punishment for them has been established in eternity," though this is debatable. That it is attached to "has come to pass" is supported by His saying: "Indeed, those upon whom the word of your Lord has come to pass will not believe." Abu Hayyan reported that the meaning is the word which Allah Almighty spoke upon the tongues of the Messengers—peace be upon them—regarding monotheism and other matters, and its proof has become manifest; but this, as you can see, is [a weak position].

(So they) i.e., the majority, (do not believe) in your warning to them. The fa (so) is for tafri' (derivation/consequence), applied to a ruling that is a result of what preceded it. It signifies that the establishment of the word against them is a cause for their denial and disbelief, and it is a cause for it in consideration of the precedence of [Divine] knowledge regarding their evil choice and their state in the reality of things. For His knowledge—Exalted is He—does not attach to things except as they are in themselves. Its final outcome is that their evil choice and their state in the reality of things is the cause of their denial and lack of belief after the warning. Thus, there is neither pure compulsion here, nor is the "known" a subordinate of "knowledge."

Some have said: The fa is either for tafri' (consequence), and the fact that the establishment of the word is a cause for their lack of belief is built upon the premise that the "known" is a subordinate of "knowledge"; or it is for ta'lil (causality), signifying that the lack of belief is the cause for the establishment of the word, based on the premise that "knowledge" is a subordinate of the "known." Compulsion is not necessitated by either approach. As for the second, it is manifest; and as for the first, it is because knowledge is not—according to those who hold this view—an independent cause, but rather their choice and their acquisition have an entry into it. So reflect upon this.

The tafri' (consequence/derivation) is what I incline toward.