John Calvin Commentary 1 Corinthians 7:31

"and those that use the world, as not using it to the full: for the fashion of this world passeth away." — 1 Corinthians 7:31 (ASV)

And they that use this world. In the first clause there is the participle χρώμενοι (using); in the second, there is a compound of it—καταχρώμενοι (abusing). Now the preposition κατά, in composition, is generally taken in a negative sense, or at least denotes intensity. Paul, therefore, directs us to a sober and frugal use of things, such as will not hinder or slow our progress, but will allow us always to hasten forward toward the goal.

For the fashion of this world passeth away. With this term, the Apostle has elegantly expressed the vanity of the world. “There is nothing,” he says, “that is firm or solid, for it is a mere show or outward appearance, so to speak.”

He seems, however, to have alluded to theatrical representations. In these, when the curtain is drawn up in a single moment, a new appearance is presented. Then, those things that held the spectators' eyes in astonishment are immediately withdrawn from their view.

I do not see why Erasmus preferred the term habitus (form). He certainly, in my opinion, obscures Paul’s doctrine, for the term fashion is tacitly opposed to substance.