Adam Clarke on 1 Corinthians 7:31

And they that use this world - Let them who have earthly property or employments discharge conscientiously their duties, from a conviction of the instability of earthly things. Make a right use of every thing, and pervert nothing from its use. To use a thing is to employ it properly in order to accomplish the end to which it refers. To abuse a thing signifies to pervert it from that use. Pass through things temporal, so as not to lose those which are eternal.

For the fashion of this world - Το σχημα του κοσμον τουτου signifies properly the present state or constitution of things; the frame of the world, that is, the world itself. But often the term κοσμος, world, is taken to signify the Jewish state and polity; the destruction of this was then at hand, and this the Holy Spirit might then signify to the apostle.