In the spiritual battle, it's absolutely critical that we understand...
#1 - What to defend: Our hearts (v.14)
#2 - How to defend: Righteousness (v.14)
a) What Christ has done on the cross (2 Corinthians 5:21)
b) How Christ has called me to live (Ephesians 4:1-3 Romans 13:12)
c) Allowing sin in our lives does 2 things:
i) Makes room for the devil (Ephesians 4:26-27)
ii) Steals the joy of my salvation (Psalm 51:12)