Your question caused me to wonder why Paul didn't just say, "...your feet shod with the gospel of peace"? Why is there a Greek word hetoimasia, before 'of the gospel of peace'? This is variously translated as "preparation" or "readiness" or "equipped". Given that to be prepared links in perfectly with being ready, and ready for action in this instance, the need is to understand what preparation is meant.
This might be grasped from Paul adding that he (who certainly is so prepared) is an 'ambassador' (vs.20) and that he needs prayer in order that he may speak boldly. Now that Greek word for 'ambassador' is presbeuo, and in the Greek East that term indicated the Emperor's Legate. In Paul's case, he views himself as the Legate of the Prince of Peace, and his task is to declare the good news, or gospel, of this One. He is speaking as the spokesman on earth of the One in heaven, the King of Kings, and Lord of Lords. This is what all Christians are to do, for Paul speaks of all Christians likewise:
"Now then we are ambassadors for Christ, as though God did beseech you
by us: we pray you in Christ's stead, be ye reconciled to God" (2
But these ambassadors for Christ are up against it, for their attempts to declare the gospel of peace in Christ attracts the full enmity of the evil one, who uses every trick in the book to attack them, to bring them down so that they become wounded soldiers, crippled and so prevented from marching forth with this gospel of peace. Hence the metaphor of putting on the full armour of God.
This brings us back to the idea of feet shod, with shoes. Yet (I repeat), Paul does not just say we must have our feet shod with the gospel of peace. He says we must have our feet shod with the preparation of this gospel of peace. Just a few verses on, Paul gives us the vital clue - he asks for prayer, that he might be able to boldly speak forth this gospel of Christ. And, supremely, he ends the description of putting on the full armour of God with,
"Praying always with all prayer and supplication in the Spirit, and
watching thereunto with all perseverance and supplication for all
saints" (vs. 18).
Therefore, Ephesians 6:18 & 19 shows that prayer is the vital preparation - both before setting forth in our role as ambassadors for the Prince of Peace in a hostile world, during our proclamation of the gospel (that we speak the biblical gospel without any man-made additions or subtractions), and after we have discharged our duty as faithful soldiers of Christ (that this gospel message will result in souls saved, by the grace of God and for his glory). Prayer equips us. Prayer protects us. Prayer empowers us. To be 'covered' in and by prayer is the preparation all soldiers of Christ need to engage in spiritual warfare that gets us through the enemy lines designed to stop the gospel of peace being heard.