As early as the fifth century A.D., Roman Catholic theologians such as Jerome were teaching that each human had an angelic being assigned to him or her, from birth, in order to protect them (Guardian Angels article in 1913 Catholic Encyclopedia).
In 1608, Pope Paul V set aside a special feast day on the church's religious calendar dedicated to honoring guardian angels. The belief in such protector angels was reaffirmed, in recent history, in an address on "Easter Monday" by the Pope ('Regina Caeli,' March 31, 1997).
Judaism states that guardian angels do exist and that each person has one assigned to him or her (Adam Clarke's Commentary). Jews also teach that each of the seventy peoples or nations mentioned in Genesis 10 (the "table of nations") had an angelic being assigned to them, with the archangel Michael assigned the task of protecting Israel (1906 Jewish Encyclopedia).
The responsibilities of guardian angels to guide the affairs of humans is considered so important that it is believed God will punish them before the sinning humans under their care (Cant. R. viii. 14; Mek., Beshallaḥ, Shirah, ii.).
The term "guardian angels" cannot be found anywhere in the Old or New Testaments. The primary "proof text" used for this belief are Jesus' words in Matthew 18:10 (see also Mark 9:33 - 50). The context of this text is that Jesus is being asked who is the greatest person in God's kingdom by his disciples (Matthew 18:1).
Jesus directly confronts the still carnal attitudes of his disciples by stating the following.
And after calling a little child to Him, Jesus set him in their midst, And said, "Truly I say to you, unless you are converted and become as little children, there is no way that you shall enter into the kingdom of heaven . . .
Take heed that you do not despise one of these little ones; for I tell you that their angels in heaven continually look upon the face of My Father . . ." (Matthew 18:2 - 3, 10).
Christ used a little child as a living illustration of the humility required for salvation. It is an attitude that must exist in those newly converted and deepened as they live their lives. He then continues to use children ("little ones") to symbolize new believers in him when he warns them not to cause any of them to be "offended" (Matthew 18:6).
These verses in Matthew are not referring to young children who are Christians, in part because Scripture does not condone the baptizing of infants or children. Jesus is, instead, calling attention to how all those in his church should not be treated, especially new believers some may consider "the least."
It is in the above context that he makes the statement some use to "prove" God assigns guardian angels to children. In his eyes there is no rank or hierarchy, no one "greater or lesser" among his spiritual children. Because He cares for all those who have faith in him and his Son, he utilizes his angelic host to serve all those "who are about to inherit salvation" (Hebrews 1:14).
While some Biblical commentaries seem to support the teaching of dedicated guardian angels many others do not. Barnes' Notes on the Old Testament states that God does not assign a dedicated spirit being to each converted person but rather has his whole heavenly army protect them (comments on Psalm 91:11).
MacArthur's New Testament Commentary states, "Neither of these texts (Matthew 18:10, Hebrews 1:14), however - nor any other Scripture - teaches the idea of an individual guardian angel for every believer, as Jewish tradition in Jesus' day taught . . . "
Easton's Dictionary concurs with this assessment on angels when it says, "The passages (Psalm 34:7, Matthew 18:10) usually referred to in support of the idea that every individual has a particular guardian angel have no such meaning."
The primary responsibility of almost all righteous spirits is to serve Christians who are to "inherit salvation" (Hebrews 1:14). Believers are watched over and protected by many righteous spirit beings, and not just one (Psalm 91:11 - 12), all of whom have direct access to the Father (Revelation 5:11). Evidence proving guardian angels are assigned to every human is sorely lacking.