10 Finally, be strong in the Lord and in the strength of His might. 11 Put on the full armor of God, so that you will be able to stand firm against the schemes of the devil. 12 For our struggle is not against flesh and blood, but against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places. 13 Therefore, take up the full armor of God, so that you will be able to resist in the evil day, and having done everything, to stand firm. (Ephesians 6:10-13 NASB)
Before believers mature to the point where they can consistently mortify the sins that so easily ensnare them, they are not a serious threat to Satan and his subordinates in his war against God. However, when believers have matured so that they continually seek to grow in their knowledge of and obedience to the Word and to serve the Lord more faithfully they will soon discover that their walk before the face of God, serving Him, and living for His glory becomes more difficult instead of easier.
This difficulty is part of the battle against the rulers, against the powers, against the world forces of this darkness, against the spiritual forces of wickedness in the heavenly places. When believers become Spirit-filled, growing in Christ-likeness, they come under attack by our enemy because his goal is to rob God of His glory and those believers are living in such state of grace that their lives bring glory to God more and more as they obey Him in every part of their lives. Of course God uses the ensuing battle both for His glory and the edification of His saints as well.