Finally, my brethren, be strong in the Lord, and in the power of his might. Put on the whole armour of God, that ye may be able to stand against the wiles of the devil. For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places. Wherefore take unto you the whole armour of God, that ye may be able to withstand in the evil day, and having done all, to stand. Stand therefore, having your loins girt about with truth, and having on the breastplate of righteousness; And your feet shod with the preparation of the gospel of peace; Above all, taking the shield of faith, wherewith ye shall be able to quench all the fiery darts of the wicked.
Why are we told to put on the whole armour of God so that we may be able to withstand in the evil day if we are raptured out before the evil day? This is not just any evil day. Paul was preparing people for the antichrist. He knew Christ would not return until the evil day happened and that we must stand firmly in the gospel until Christ returns. We need to take this teaching and prepare people of our day so that we may all withstand when the evil day comes.