Zechariah 1:13

And the LORD answered the angel that talked with me with good words and comfortable words.

The angel pleaded for mercy toward Jerusalem and Judah, asking how long mercy would be withheld after seventy years of trouble, and the Lord answered that plea. His answer was given in good and comfortable words of reassurance that declared His compassion and that He had returned to Jerusalem with mercy. The answer promised restoration, that the temple would be rebuilt and that Jerusalem and the cities of Judah would again prosper.

These assurances were given to strengthen and encourage His chosen people in their crisis when they were uncertain whether they could continue rebuilding. The comforting words introduced an illustration contrasting Satan's work with Christ's work, showing that Christ as their Mediator has power to defeat the one who accuses them. This strengthening came while Satan sought to weaken the people by emphasizing their imperfections.