matthew 1:20 But while he thought on these things, behold, the angel of the Lord appeared unto him in a dream, saying, Joseph, thou son of David, fear not to take unto thee Mary thy wife: for that which is conceived in her is of the Holy Ghost. - Free Bible Online

      20. But while he thought on these things--Who would not feel for him after receiving such intelligence, and before receiving any light from above? As he brooded over the matter alone, in the stillness of the night, his domestic prospects darkened and his happiness blasted for life, his mind slowly making itself up to the painful step, yet planning how to do it in the way least offensive--at the last extremity the Lord Himself interposes.
      behold, the angel of the Lord appeared to him in a dream, saying, Joseph thou son of David--This style of address was doubtless advisedly chosen to remind him of what all the families of David's line so early coveted, and thus it would prepare him for the marvellous announcement which was to follow.
      fear not to take unto thee Mary thy wife, for that which is conceived in her is of the Holy Ghost--Though a dark cloud now overhangs this relationship, it is unsullied still.

JFB.