All Scripture is inspired by God and is useful for teaching
2 Timothy 3:16 

God so love the world that He gave His only Son, so that everyone who Believes in Him might not perish but might have eternal life
John 3:16

Put on the armor of God so that you may be able to stand firm against the tactics of the devil
Ephesians 6:11

Where two or three are gathered together in my name, there am I in the midst of them.
Matthew 18:20