" Many interpreters try to list prayer as one of the items in the armor, along with truth, righteousness, peace, faith, salvation, and the Word of God. That won’t work, however, because every other item is likened to something like a helmet, sword, or breastplate. When he comes to the end, he just says pray, pray, pray in the Spirit, pray with alertness, pray all kinds of ways, pray all the time. "

― Timothy J. Keller , Prayer: Experiencing Awe and Intimacy with God