Adam Clarke on Luke 1:14

Thou shalt have joy, etc. - ΕϚαι χαρα σοι, He will be joy and gladness to thee. A child of prayer and faith is likely to be a source of comfort to his parents. Were proper attention paid to this point, there would be fewer disobedient children in the world; and the number of broken-hearted parents would be lessened. But what can be expected from the majority of matrimonial connections, connections begun without the fear of God, and carried on without his love.

Many shall rejoice at his birth - He shall be the minister of God for good to multitudes, who shall, through his preaching, be turned from the error of their ways, and converted to God their Savior.