2 Corinthians 11 Pray that the Holy Spirit gives you the words to speak!

12But what I am doing I will continue to do, so that I may cut off opportunity from those who desire an opportunity to be regarded just as we are in the matter about which they are boasting. 13For such men are false apostles, deceitful workers, disguising themselves as apostles of Christ. 14No wonder, for even Satan disguises himself as an angel of light.15Therefore it is not surprising if his servants also disguise themselves as servants of righteousness, whose end will be according to their deeds.

Have you ever been home and then you hear the doorbell ring? Standing outside are two men in plain suits exposing a gospel that doesn't believe Jesus is God, not part of the Trinity and if you examine their bible you find all references to Jesus as God have been removed or changed!
They are misguided souls that cannot go to heaven because of their unbelief even though they perform many good works for their fellow man.
Was is an angel of light that swayed then from the one true God? You can bet it was, Satan himself.

Be prepared as Paul was, understand and study the Bible and  when your doorbell rings pray the Holy Spirit gives you the words to speak.

Blessings, David 

Scripture blog; http://stanfordsancutaryscripturestudies.blogspot.com