Christian Mysticism has often syncretized with Wicca and the likes. Powerful and advance barrier spells sometimes require a kind of minor deity to follow you around, or in much crueler terms; "enslave" if you are a witch or warlock of that prowess, just like a an animal familiar.
This requires a bait shrine; where you direct the worship of these minor deities or demons and convert it into your own magickal power. At that point, the displaced deity or demon loses strength and comes down (or up) to confront you. The means of their enslavement or pledge to you as your familiar is up to you. Though it is severely weakened due to it's lack of devotion from it's worshipers, most inexperienced witches are no match despite such. This is the reason why deities are deities. They are powerful spirits that has been able gain worship and retain it through the millennia. Though this "deity fishing" is highly dangerous and is not recommended. But if you refuse to pass up the chance to have a somewhat powerful entity to be your assistant; crack open a grimoire for instructions, find that shrine, sharpen your athame and get ready for a scrap.
But this is near impossible, for the means of this deity fishing has been lost to the eons.
Back to the original topic; christian faithfuls and mystics need not the assistance of puny deities or demons. Their all powerful deity is all they need. The process as goes...
One must follow strict, monk like prayer and faith. No specific religious instruction; just pure, meditative, faithful prayer. Of any kind..
Then you must devote yourself to your powerful deity ( in my case the Judaeo-Christian God the Father). This makes you closer to him and although no one is outside the circle of God's love, the closer you are; the stronger your barrier.
Note: Faith and Energy are one and the same. Both are needed to execute spells and barriers.
When I say "Circle of God's Love" it is far from just being a metaphor. It is an actual barrier present in all of us. Nourishing this barrier requires faith. This is why in many stories, monks and faithfuls are often shown going toe to toe with demons and sometimes even Satan himself. And old saying "A monk takes flight before the devil does."
One of the most famous stories is that of my Patron Saint, St. Dunstan. While working on a grail for the mass in the monastery's foundry, the devil appeared behind him. The old saint was not a bit scared and was a little annoyed. The devil, refusing to leave and to cease vexating the old saint, St. Dunstan got a pair of red glowing pinchers and yanked down the devil's nose. Refusing to let go of his shnotz until he agreed to leave and never show his face to him again, the devil agreed. After releasing him, the devil went make on his word. St. Dunstan; already seething in anger, threatened to clamp down and coat the devil's privates with molten brass. Moral of the story; don't mess with old monks and faith is the spiritual adrenaline.
The last part is to put trust and faith to practice. Leaps of faith are great examples of this. Do not attempt anything suicidal though, but try to prove your faith through grueling perseverance or sudden and cunning acts of bravery. These are more than enough to solidify your holy armor and would make any entity of ill omen think twice before confronting you.