It's called "the Armor of God" because its components are not of our own making, but are the gift of God. Some wrongly credit the "shield of faith" to themselves, but this is a recipe for defeat against the flaming arrows of the evil one. Only a supernatural, God-given faith can withstand those assaults. We rob God and indeed even rob ourselves of great resources in the Christian life when we ascribe any of them to ourselves and not to Christ alone. (Eph 6:10-18)
Scripture frequently refers to the the LORD as our shield (Gen. 15:1; Ps. 5:12; Prov. 30:5), so when we take up the shield of faith it means we rest in the Lord ... in Christ Himself.
The Holy Spirit has joined us to Christ and our supernatural faith is like a shield because it continually lays hold of Christ who covers us with His righteousness which makes us immune to the attacks of Satan. Satan paces around the earth hoping to falsely accuse the brethren as being not worthy of the kingdom of God. Of course if we remembered our own record, he would be right, Of ourselves, in armor of our own crafting we have no defense against Satan's fiery darts. And if we ascribe the shield of faith to something we muster up in the flesh we would be unprotected and completely open to his attacks. But the shield of faith is not something we have to muster up ... it is a piece of armor the Lord has given us to use Only Christ our shield protects us.