God has provided gifts to the believer's for the growth and edification of the body of Christ (The Church). Ephesians 4:16 "...from whom the whole body, joined and knit together by what every joint supplies, according to the effective working by which every part does its share, causes growth of the body for the edifying of itself in love." In Romans 12 the list of these gifts is given in this order: Prophecy, ministry, teaching, exhort, giver, leader, mercy. One may say that people have these characteristic without having Christ as their personal Savior, but the gift that comes from God enables one to act with these characteristics beyond what the natural man is able. These gifts can only be seen in one's life as one is yielding to the Spirit of God.
Not every body has the same measure of spiritual gift given to them (One may say his gift is ministry and another's may be mercy). In Romans 12:6 it says, "Having then gifts differing according to the grace that is given us, let us use them." God in His infinite wisdom and knowledge knows what is needed in each person. I believe that all of these gifts can be seen in one believer's life the more he grows in Christ (Like one cannot separate the attributes of God from one another, you cannot really have one spiritual gift without the other complimenting it... Made in the image of God I guess). I also believe that God may change one's prominent gift according to what is needed for the further growth of the body of Christ (One's atmosphere may change from many believers to just a few such as going from the States to a sparse mission field).
It is beneficial to know your spiritual gift so you may know how you can best serve others in the body of Christ, but you do not need to know what your spiritual gift is in order to use it. As long as you are yielding your life to Christ your spiritual gift will become evident as you use it and naturally edify the other believers with it. The first three Chapters of Ephesians talk of our position from the natural man to the new man... reading this and understanding what Christ has done for us should provoke the desire to grow in Him and share with others about the grace and mercy He has given to us. Reading the last three Chapters of Ephesians show how we "walk" through life, but as you read it you will see how the spiritual gifts that God gives us plays a huge role in our walk and interaction with those around us.