Is it a sin to wear polyester blends, etc?

The law concerning mixing various things represents Israel being called apart from the world. But in prophetic recapitulation, the separation of Israel is also a metaphor for not mixing law and grace, or the heavenly and the earthly.

In Revelation when the luke warm is spewed out, it is the same picture of mixing. It makes no sense to say that God would prefer that we be good or evil, but not in between. Christ fulfills the laws against mixing by reconciling law and grace, and the heavenly and the earthly. For this he dies on the cross.

This law is intended as a prophecy of Christ. As a mere allegory, it has no moral meaning outside of Israel's call to be a witness by living 'dinner theater' as a lesson for us all.