The beginning of the gospel - The word “gospel” literally signifies good news, and particularly the good tidings respecting the way of salvation by the Lord Jesus Christ. Some have understood the word “gospel” here to mean “history” or “life - the beginning of the history,” etc.; but Mark says nothing of the early life of the Saviour. The word “gospel” here has reference rather to the preaching of John, an account of which immediately follows, and means the beginning of the good news, or annunciation respecting the Messiah. It was very customary thus to prefix a title to a book.
The Son of God - This title was used here to attract attention, and secure the respect of those who should read the gospel. It is no common history. It does not recount the deeds of man - of a hero or a philosopher - but the doctrines and doings of the Son of God. The history, therefore, “commands” respect.