We have a very real enemy. He is a master of deception and subversion. He knows how to hit us where it counts, and how to deceive us into sin. He has been fighting against mankind for millennia. He is more powerful, more experienced, and more cunning than we are. He is dedicated to seeing us fall. He wants us to fail.
1 Peter commands us, "Be sober, be vigilant; because your adversary the devil, as a roaring lion, walketh about, seeking whom he may devour:" This warning tells us that we must be serious about the battle with sin. It also commands us to watch. We must be ready to fight off the attacks of our enemy, the devil. But we cannot win the battle by ourselves. If we are to be successful in the Christian life we must be focused on Christ. Only by Him can we gain the victory.
God will be with us in the fight. As He promised Joshua, "Be strong and of a good courage; be not afraid, neither be thou dismayed: for the LORD thy God is with thee whithersoever thou goest." Whenever we find ourselves struggling, we can call upon Him. He will be a shield unto us. He will fight for us. He will be the one to deliver us from our enemy. It is up to us to remember His promises, and the victory He has won over our already defeated enemy. If we rely on Christ for our strength, He will not allow us to be overcome.
"Fear thou not; for I am with thee: be not dismayed; for I am thy God: I will strengthen thee; yea, I will help thee; yea, I will uphold thee with the right hand of my righteousness." – Isaiah 41:10