One of my favourite symbols in the Old Testament is the construction and care of the temple. Particularly when Solomon builds it. I’m always flabbergasted by how much detail goes into building the temple (both Solomon’s permanent one and the moving one from the Exodus) and the riches that go into the temple. I love this symbol/imagery because today we are the new temples. So when I read the OT passages, I can reflect on how much MORE detail God put into me and how much MORE valuable he finds me than the temple filled to the brim with gold and expensive woods and jewels.
It is no wonder then, that in 2 Corinthians 6:14-18 Paul tells us to not associate ourselves with things that are opposite to what God has called us to. Paul is quoting from Leviticus for part of it, which is where God originally commands the Israelites to be holy because he is holy (11:44). We have to protect ourselves and continue to set aside our lives to follow him (picking up our crosses, anyone?)
Does this mean we don’t associate with non-believers? No. I can’t reconcile that with the life of Jesus who himself spent countless hours reaching out to those who were called “sinners”. I think it is more that we choose not to strongly attach ourselves to non-believers because it is much easier for them to pull us down to sin than for us to pull them up into righteousness. That doesn’t make it easy, but as God’s ambassadors (2 Corinthians 5:20) we continue to live in a way that shines his light to the world.