The prophet Joel is going to teach the people how to give thanks to God when he comes with promises. First, you may let go of your fear (cf. Joel 2:2, Joel 2:6). God’s punishments scares you, so that you might think: what else is going to happen, what other disasters will affect us? Let go of that fear! God’s love gives us peace!
Subsequently, Joel teaches that you can trust God completely. He speaks as if God’s promises have already come to pass. Note that in Joel 2:21–24 Joel constantly switches from the present to a past or a completed tense. In the present you may let go of your fear and be glad (Joel 2:21a, Joel 2:22a, Joel 2:23a), for God has given promises! When God grants promises you can be so certain of the fulfillment of those promises that you begin to look at parched deserts as if they have already turned green, at bare trees as if they are already bearing abundant fruit, at famine-stricken areas as if the rain you so desperately wish for has already fallen abundantly and the threshing floors and pressing vats are overflowing with a new harvest. You may be so sure of God that you can exclaim: the Lord has (already) done great deeds. When God makes promises, you may live in that confidence.
21 “Fear not, O land; be glad and rejoice, for the LORD has done great things!