Read Ephesians 6:10-18
The armor is not to be put on and taken off periodically but to be put on and left on. The armor is actually an attitude of faith; therefore, it is something that is put on by an act of the will and left on.
As we mature in the Christian life, we will discover areas in our lives where our faith is not as strong as it should be; that is, the armor is weak in a certain place.
At such a time, our responsibility is to go to the Word of God to study His promises concerning our area of weakness so that our faith will be strengthened.
Notice the parallel between Ephesians 6:11, "Put on the whole armour of God," and Romans 13:14, "Put ye on the Lord Jesus Christ." God's provision for victory is in the Person of the Lord Jesus Christ and through the Word of God.
In putting on the Lord Jesus Christ, we need to remember that the living Word (Jesus Christ) is revealed through the written Word (the Bible).
In His prayer for His own, Jesus prayed, "Sanctify them through thy truth: thy word is truth" (John 17:17). We put on the Lord Jesus Christ as we study the Word of God and obey what it says. The believer's armor, then, is not physical protective equipment, but is Jesus Christ Himself.
Putting on Christ is similar to what we are told in Ephesians 4:24: "Put on the new man." This new man is Christ formed in the believer. Paul was greatly concerned that this be true of every believer, and he told the Galatians: "I travail in birth again until Christ be formed in you" (4:19).
"And that ye put on the new man, which after God is created in righteousness and true holiness" (Eph. 4:24).