Zech. 1:13,17 And the LORD answered the angel that talked with me with good words and comfortable words....the LORD shall yet comfort Zion, and shall yet choose Jerusalem.

Life in this world throws a lot of discouraging things at people. Those returned exiles were discouraged and disheartened. They did have a desire to know and worship God, but conditions seemed to work against them. That's how it is with many of us today.
What they needed most at this particular time were kind words of comfort and encouragement.

And God gave them good and comforting words.

Isaiah 40:1 Comfort ye, comfort ye my people, say your God.
40:2 Speak ye comfortably to Jerusalem...her iniquity is pardoned:
40:28 Have you not known? have you not heard, the everlasting God, the LORD, the Creator of the ends of the earth, faints not, neither is weary? there is no searching of his understanding.
40:29 He gives power to the faint; and to [them that have] no might he increases strength.
40:30 Even the youths shall faint and be weary, and the young men shall utterly fall:
40:31 But they that wait upon the LORD shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint.