I came across the following from John Henry Newman (1801-1890) sometime ago. It forms part of a larger series of meditations on Christian doctrine that can be found at 'newmanreader.org'.
"God has created me to do Him some definite service; He has committed some work to me which He has not committed to another. I have my mission—I never may know it in this life, but I shall be told it in the next. Somehow I am necessary for His purposes, as necessary in my place as an Archangel in his—if, indeed, I fail, He can raise another, as He could make the stones children of Abraham. Yet I have a part in this great work; I am a link in a chain, a bond of connexion between persons. He has not created me for naught. I shall do good, I shall do His work; I shall be an angel of peace, a preacher of truth in my own place, while not intending it, if I do but keep His commandments and serve Him in my calling."