2 Cor 6:14 is best illustrated in the life of Jehoshaphat and his association with Ahab.  Jehoshaphat typifies the believer, 2 Chr 17:1-6.  Ahab typifies the unbeliever.  When you are unequally yoked:

You bring ungodly influences into your house.  Jehoshaphat joined affinity with Ahab, 2 Chr 18:1.  When he did this, he brought Ahab’s evil influences into his house, 2 Chr 21:1, 5-6, 11-15.

You make bad decisions based on association.  Jehoshaphat was persuaded to go along with Ahab, 2 Chr 18:2-3, in a battle he should have never fought.  He inquired of the Lord as an after-thought, 2 Chr 18:4.  Jehoshaphat typifies a true believer.  

He could discern between the “good” report of the false prophets and the true report of Micaiah.  Ahab didn’t like him because Micaiah never prophesied “good”, 2 Chr 18:7.  But Ahab neglected to say that he always prophesied true!!  

In the inquiry, Jehoshaphat learned that Ahab would die, v.16.  And Micaiah explained just how the Lord deceived the false prophets with a lying spirit.  Nevertheless, Jehoshaphat went into the battle, 2 Chr 18:28.  This was a terrible decision and clearly against the Lord’s will.

You lose your godly influence in their lives.  2 Chr 18:28, Jehoshaphat lost his ability to turn Ahab away from his plan.  He had already agreed to go with him.  He could have tried to stop Ahab from going into battle.  However, he didn’t because his association with Ahab was connected with an ulterior motive.  

These two kings were reuniting the divided kingdom.  If Ahab fell in battle, Jehoshaphat would become the king of both nations.  And in 2 Chr 21:2, he did.  

When you know the word of God and you are associated with those who don’t know it or believe it, be careful going along with them, no matter your motive.  Your association may convince them to continue down a path that will ultimately destroy them.

You put yourself directly in harms way.  2 Chr 18:29-31.  If the Lord had not stepped in to help him, Jehoshaphat would have been a dead man.  

I am reminded of some church kids who went joy riding with a couple of their lost friends one night.  They died that night when their car flipped and caught on fire.  Christian kids often end up taking drugs, drinking alcohol, and getting into harmful trouble when they start running with the wrong crowd.

You jeopardize your own relationship with the Lord.  2 Chr 19:1-2, wrath was upon Jehoshaphat from the Lord.  And it only got worse, 2 Chr 20:34-37.  When you are unequally yoked, your relationship with the Lord will suffer.