'In the Faith' in the Bible

Paul an apostle of Jesus Christ, by the divine appointment to the converts which are at Ephesus, who stand firm in the faith of Christ Jesus:

until we all reach oneness in the faith and in the knowledge of the Son of God, [growing spiritually] to become a mature believer, reaching to the measure of the fullness of Christ [manifesting His spiritual completeness and exercising our spiritual gifts in unity].

Therefore, put on the full armor of God, so that you can withstand [the devil, See verse 11] when the evil day comes. And, after you have done everything you can, still remain standing firm [in the faith].

So, you people should stand firm [in the faith], with the belt of truth firmly buckled around you, and with the "flack jacket" of righteousness on your chest.