Pope Benedict gives, in his new book, three providential reasons for this title of our Lord: "of Nazareth."
1. Jesus is the perfect "Nazirite," meaning His essential and indelible supernatural consecration by the natural divine union of the Son with the Father. "He was no Nazirite in the classical sense of the term. Nevertheless, it could be said of him, in a manner far surpassing such external details, that he was totally consecrated to God, completely made over to God, from his mother's womb to the day of his death." p. 116
3. Nazareth was his hometown, hence the Roman title on the Cross.
This thought came to mind in light of today's readings regarding the miraculous conception and divine pre-conception election and consecration of Samson (Judges 13) and Saint John the Baptist (Luke 1) both cited by the Holy Father's book.