Tafsir of Al Imran 3:137

(There have passed away): That is, they have elapsed.

(Before you [many] ways [Sunan]): That is, events that occurred among the nations who denied [the truth]. Allah the Exalted executed them according to His customary practice. Al-Mufaddal said: The intended meaning is "nations," as the word Sunnah has been used to mean "nation" in their speech. From this is the saying: "People have not witnessed a virtue like your virtue, nor have they seen the likes of you among the bygone Sunan (nations)." 'Ata’ said: The intended meaning is "laws and religions." Thus, the meaning is: "There have passed away before you laws and religions that were abrogated."

It is not hidden that the first [interpretation] is more appropriate for the context. This is because this [verse] is either meant to urge those held responsible—or those who consume usury—to perform acts of obedience, or to repent from disobedience, or both, in a manner different from what preceded, as has been said. Or, it is a return to detailing the remainder of the story after laying the foundations of guidance and righteousness and arranging the prerequisites for success and prosperity, according to one opinion. Mentioning that religions have passed away does not have much connection to that, even though some claim that it contains a reinforcement for the believers to remain steadfast upon the religion of the Prophet (may Allah bless him and grant him peace), so that they do not weaken due to the Jews claiming that the religion of Moses (peace be upon him) cannot be abrogated and that abrogation is not permissible for Allah the Exalted because it is bada’ (a change of mind). It also serves as an incitement for the Jews, urging them to accept the religion of Islam, and a warning to them that the same fate might befall them as befell those who denied [the truth], and a strengthening of the hearts of the believers with the [assurance] that He will grant them victory over the deniers.

Yes, applying the term Sunnah to a "law" (shari’ah) is closer than applying it to an "event" (waq'ah), because it originally refers to a path or a custom, as in their saying: "The Sunnah of the Prophet (may Allah bless him and grant him peace)." The prepositional phrase is either connected to khalat (passed away) or to a deleted [predicate] acting as a state (hal) of Sunan—meaning "ways existing before you."

(So travel through the earth): That is, with your feet or with your understanding.

(And observe): That is, reflect.

(How was the end of the deniers): That is, the final state to which their denial of their prophets led them. The Fa (so) is to signal that the passing [of those nations] is the cause for the command to travel and observe. It is said: The meaning is conditional—that is, "If you are in doubt, then travel," etc. The address, in any case, is directed to the believers. An-Naqqash said: [It is addressed] to the disbelievers, but there is remoteness in that.

Kayfa (how) is a predicate placed at the beginning [of the clause] that acts as an interrogative suspended by the verb of observation. The sentence is in the position of the accusative after the removal of the preposition, because the standard [grammatical] usage is to employ it with a preposition. The verb is stripped of the feminine ta because the subject is metaphorically feminine.