In popular culture, it is believed that holy objects, such as garlic, crosses, and holy water, can protect against evil, like vampires. Also, Caleb's response to this question inspired me to ask whether or not using those things (garlic, crosses, and holy water) have any legitimate basis in Christian practice, or whether or not they are merely idols and only part of the fictional world.
In Catholic Tradition and culture, vampires only exist in scary novels/movies, and garlic is only used for seasoning delicious meals.
However, crosses, holy water, and various other holy objects and gestures can be ordained by the Church as sacramentals.
Sacramentals are material objects, things or actions (sacramentalia) set apart or blessed by the Roman and Eastern Catholic Churches, the Eastern and Oriental Orthodox Churches, the Church of the East, the Anglican Churches, the Independent and Old Catholic Churches, and the Lutheran Churches to manifest the respect due to the sacraments, and so to excite pious thoughts and to increase devotion, and through these movements of the heart to remit venial sin, according to the Council of Trent (Session XXII, 15).
Sacramentals are sacred signs which bear a resemblance to the sacraments. They signify effects, particularly of a spiritual nature, which are obtained through the intercession of the Church. By them men are disposed to receive the chief effect of the sacraments, and various occasions in life are rendered holy.
The Rituale Romanum clearly defines the order in which a priest or deacon may bless a sacramental. Sacramentals such as crosses, holy water, and blessings are employed during most rituals in the Catholic Church. These rituals range anything from Baptism (which itself is a protective exorcism) to weddings to demonic exorcisms.
Yes, the Catholic Church performs hundreds of real exorcisms every year. Demonic possession in the Church is very real, and sacramentals have been used since apostolic times to battle evil spirits.
But don't be fooled by over-blown Hollywood concoctions of "head-spinning" myths and "green vomit" superstitions about how the Catholic Church supposedly performs exorcisms.
The most realistic and accurate portrayal one will find of how the Catholic Church performs the rite of exorcism is The Rite with Anthony Hopkins.
The Catholic Encyclopedia says about sacramentals:
Its important to recognize that sacramentals, such as crosses and holy water, are not magical. They are not idols. They are simply material objects that are connected to the heart of the Church (the 7 sacraments instituted by Christ) via the ordaining power of the Holy Spirit and are entrusted to the priesthood of all believers for both edification and protection.
All sacramentals draw their power from Jesus Christ...who is God.
And from my personal experience, garlic is only effectively used when its sprinkled on buttered toast.
The Book of Concord is the seminal collection of Lutheran doctrine. The only power it claims that garlic has is to temporarily reduce the power of magnets:
There is a basis for sacramental items, but even those items can become idols. Below is part of the scripture that talks how items like handkerchiefs that were brought from Paul carried power of God to heal the sick. As in regards to power to ward of evil spirits there is no basis for that the bible.
As seen in verse 15 that evil spirit was not even afraid of even of "name of the Lord Jesus". Just because Jesus had authority to exercise demons it does not mean that any person using the name of Jesus can do the same. Just because you bring some items with you that have been "prayed over" (I don't like to use word blessed) it does not guarantee protection or ability to exercise demons.
Items it self has no power no matter if it is a cross, handkerchief or anything else. The power comes from God and if you have His power in you than you have no need for any items. Read 1 John 4:4 that I quoted below. Displaying or carrying a cross with you or even yelling the name of Jesus will not send demons away. Being born again and baptized by Holy Spirit that He now dwells in you.
In regards to idol just refer back to 10 commandments, make "no image" of wood, stone or anything else. It is pretty clear that nothing can replaces God and His Power. Anything that replaces God is an idol or His Power is an Idol.
Garlic, crosses and "holy water" have absolutely no place in the christian's spiritual life. Only Christ should have any influence upon the believer. As the Spirit, He resides in them to be their life. All these outward signs i.e crosses, "holy" water etc., do absolutely nothing to advance the spiritual growth or perfecting of the genuine christian. Only Christ Himself can do that. Trusting in anyone or anything else is a waste of time.