‘In that day it shall be said to Jerusalem,’ – this is now the church of Christ – ‘Fear thou not: and to Zion, Let not thine hands be slack’ – this is the exhortation of the New Testament church. Don't despair, don't go to pieces, don't let your hands be faint or slack, because all God's promises will be carried out.
Fear causes us to hesitate, to doubt whether our efforts will come to anything. But we are exhorted by the Lord himself not to fear. That is the same as his promise that our active hands will reap a reward and see the fruit of what they do. If our intention is to serve him and to glorify him, he will remove all the obstacles to our success, and give us the joy of being fellow-workers with him. He will allow us to join with him in celebrating what our hands have accomplished. If we are his source of joy, then he too will not allow that joy to be taken from him.
How many times the Lord picks us up and reassures us, because he knows our weakness and our tendency to faint. He is not faithful because we are strong and never feel discouraged; he is faithful for his name’s sake.