I have wondered about this before, especially when angel pins were being sold by the thousands. Where in scripture are we told that we each have a guardian angel? I can't find it.
Psalm 91:11 For he shall give his angels charge over thee, to keep thee in all thy ways.
Matthew 18:10, Christians (those who believe in Christ, are the "little ones")
Take heed that ye despise not one of these little ones; for I say unto you, That in heaven their angels do always behold the face of my Father which is in heaven.
Matthew 18:10 states, “See that you do not look down on one of these little ones. For I tell you that their angels in heaven always see the face of my Father in heaven.” In the context, “these little ones” could either apply to those who believe in Him (v. 6) or it could refer to the little children (vv. 3-5). This is the key passage when the discussion of guardian angels comes up. There is no doubt that good angels help protect (Daniel 6:20-23; 2 Kings 6:13-17), reveal information (Acts 7:52-53; Luke 1:11-20), guide (Matthew 1:20-21; Acts 8:26), provide for (Genesis 21-17-20; 1 Kings 19:5-7), and minister to believers in general (Hebrews 1:14). There are so many more instances of these in Scripture.
The question that is difficult to answer is whether each person or each believer has an angel assigned to him/her. In the Old Testament, the nation of Israel had the archangel (Michael) assigned to it (Daniel 10:21; 12:1), but you do not have anywhere in Scripture where it states that an angel was “assigned” to an individual (they were sometimes sent to individuals on different instances but no mention of “permanent” assignment is given). One commentator states that the Jews had fully developed the belief in guardian angels during the time between the Old and New Testament periods. Some early church fathers believed that each person had not only a good angel assigned to him/her but also a demon as well (I am not sure who they believed assigned the demon, whether Satan or God). But at any rate, the belief in guardian angels has been around for a long time.
If one is to understand from the Matthew 18:10 passage that guardian angels are referred to, it would seem that these angels are not in an active duty, but rather “always see the face of” the Father in heaven. The active duty or oversight seems then to come more from God than the angels. In our society today, it is “in” to believe in angels. We have movies that focus on angels; we have series on TV which portray angels as being assigned to help. Scripture makes it clear that although angels possess superhuman power and knowledge, they are created beings just as we are and are “nothing” in comparison with God. As such, they are not to be worshipped (Exodus 20:1-6; Colossians 2:18). Rather, worship is to be reserved for the Trinity alone. Unfortunately, while the shows about angels give lip service to God, the Son of God is rarely mentioned (if at all). And God says, in John 5:23 that if one does not honor the Son, he does not honor the Father who sent Him.
It cannot be emphatically answered from Scripture whether each believer has a guardian angel assigned to him/her. But as stated earlier, God does use them in ministering to us. I believe that it is scriptural to say that He uses them like He uses us, i.e. He in no way needs us or them to accomplish His purposes, but chooses to use us nonetheless (Job 4:18; Job 15:15). And in the end, whether we have an angel assigned to protect us or not, we have a greater assurance that God gives: that if we are His children through faith in Christ, He works all things together for good (Romans 8:28-30), and that Jesus Christ will never leave us or forsake us (Hebrews 13:5-6). If we have an omniscient, omnipotent, all-loving God with us, what does it really matter whether there is a finite angel along side of us or not?
Recommended Resource: What the Bible says about Angels by David Jeremiah.