True Friendship

Lately it seems as though the Lord has been bringing to my attention the idea of friendship. In particular, can believers in Yeshua/Jesus truly be friends with non-believers?
I think first we have to define the word "friend" according to the Scriptures.

"Do you see that faith was working together with his works, and by works faith was made perfect? And the Scripture was fulfilled which says, 'Abraham believed God, and it was accounted to him for righteousness.' And he was called the friend of God." - James 2:22-23
You are My friends if you do whatever I command you. No longer do I call you servants for a servant does not know what his master is doing; but I have called you friends, for all things that I heard from My Father I have made known to you. You did not choose Me, but I chose you and appointed you that you should go and bear fruit, and that your fruit should remain, that whatever you ask the Father in My name He may give you." - John 15:14-16

Moses was also called a friend of God, and as we just read what Yeshua/Jesus said to His disciples, a true friend of God is someone who is obedient to Him. A more specific definition, in accordance with Scripture, would be 'One who obeys the Lord's Torah/Law out of love for Him and by His grace through faith'.
I believe that the better we understand this concept of friendship as being defined by walking in God's commandments (His Torah), then we will better understand why Paul writes what he does to the Corinthian church.

"Do not be unequally yoked together with unbelievers. For what fellowship has righteousness with lawlessness? And what communion has light with darkness? And what accord has Christ with Belial? Or what part has a believer with an unbeliever? And what agreement has the temple of God with idols? For you are the temple of God. As God has said: 'I will dwell in them and walk among them. I will be their God, and they shall be My people." Therefore "Come out from among them and be separate says the LORD. Do not touch what is unclean, and I will receive you. I will be a Father to you and you shall be My sons and daughters, says the LORD Almighty.'" - 2 Corinthians 6:14-18

Notice the temple of God and idols, light and dark, Christ and Belial... all things that are complete opposites and have no union what-so-ever. And Paul also includes a believer and an unbeliever. We have no business being in fellowship with unbelievers. But why?
It is because of where Paul quotes from first in Leviticus 26:12 and Jeremiah 32:28.
God will dwell in and among His people only when we are holy/separate from the uncleaness of the world. Does that mean we have to be perfect before He'll dwell with us? Well, yes. But not on our own accord. It is impossible for us to be perfect on our own, but through the blood of Messiah we are made spotless!
So then, if we are born again in Him we ought not to have a relationship with those who are lawless.
He quotes from Isaiah 52:11 which exhorts us to not touch anything unclean. Isaiah was writing to those who carried the vessels of the LORD, which were the priests. According to Scripture we are priests in God's kingdom (1 Peter 2:5,9) which means we are not to be a part of this world (that which is unclean).

But what about witnessing? How are we supposed to witness to unbelievers without being friends to them? The Lord tells us that the most effective way of witnessing is to simply be obedient to His Torah/Law and walk in love for other believers (Deuteronomy 6:5; Leviticus 19:18; Matthew 5:16-19, 22:37-40; John 13:35; 1 John 5:2-3)
We have to remember that yes the Lord loved the world so much that He died to save it, and yes He wants us to be a light to those in darkness, but HE knows that if we 'hang out' with those who are immersed in sin, that lifestyle will eventually draw us into it because sin is always looking for a way to get in. In fact, the LORD tells Cain this:

"...sin lies at the door. And its desire is for you, but you should overcome it." - Genesis 4:7b

We are constantly told not to walk in the ways of the world nor to turn back to our old ways, but to keep our eyes on things above...things of the Lord.
If we truly care about the lost (and we should!) then we must do all we can to walk in obedience to the Lord's Torah/Law and show unbelievers the truth of His Word. As living epistles, we are His letter to those who are lost. If they 'read' us as we walk in accordance with His commandments and share His good news, then His Word will not return void and people will see our good works and glorify God (Matthew 5:16).
A final thought from the epistle of James on those who are friends with unbelievers and the world:
"Adulterers and adulteresses! Do you not know that friendship with the world is enmity with God? Whoever therefore wants to be a friend of the world makes himself an enemy of God. Or do you think that the Scripture says in vain, 'The Spirit who dwells in us yearns jealously?'" - James 4:4-5