One of the intriguing things found within God's Kingdom is the following concept: The ground you gain in the Kingdom of God is contested by the devil. This of course is no surprise as we, the focus of God's love, angers a jealous enemy. Through this jealousy he entices, accuses, intimidates and generally makes a nuisance of himself.
This is where 'spiritual warfare' comes in. it simply means withstanding the attacks of satan and resisting his tactics and weapons. If there was no battle to be fought, the Bible would be silent of this subject but it is not. Here is an example: 2 Corinthians 10:4-6, "For the weapons of our warfare are not carnal but might in God for pulling down strongholds, casting down arguments and every high things that exalts itself against the knowledge of God bringing every thought into captivity to the obedience of Christ, and being ready to punish all disobedience when your obedience is fulfilled."
Here is another: Ephesians 6:12, "For we do not wrestle against flesh and blood, but against the rulers, against the authorities, against the cosmic powers over this present darkness, against the spiritual forces of evil int he heavenly places".
As we withstand the attacks of the devil, we do it from the status of being "more than conquerors in Christ Jesus" (Romans 8:37).