Mark 1:1 Commentary - Vincent's Word Studies in the New Testament
without the article, showing that the expression is a kind of title. It is 'the beginning, not of his book, but of the facts of the Gospel. He shows from the prophets that the Gospel was to begin by the sending forth of a forerunner.
Consult other comments:
Vincent's Word Studies in the New Testament
Originally published in 1887, Vincent’s Word Studies in the New Testament lists each significant word in the New Testament with its meaning, derivation, idioms, and uses in a verse-by-verse commentary format.