2:19
While turning to the Lord is the right thing to do, it will also bring practical benefits as well. The Lord will bring fruitfulness to the land, and never again will they be an object of scorn among the nations. Note that it is the Lord who made Israel an object of scorn. This was not an arbitrary action, but one that was righteous judgement upon their sin. But because it was the Lord who did this, it is also the Lord who can change things.
2:20
The “northern horde” could refer to Assyria, but this is far from certain. For Assyria did get close to defeating Jerusalem, but was then miraculously defeated, as noted in Isaiah 36-39. Alternatively, it could just be a general reference to Israel’s enemies. It could also be a reference to locust hordes, though they tended to come from other directions. However, references to attacks from the north are common in the prophets. Whatever the case, the key thing is that the enemy is completely defeated, and the defeat is God’s doing. When faced with trouble we tend to turn anywhere, except the Lord, in looking for help, only turning to Him when we have exhausted every other option. We need to turn to Him more quickly, for salvation comes from the Lord.
2:21,22
Joel then addresses the land, the animals and the people in v21,22 and 23, respectively. The salvation of the Lord affects all aspects of creation. An implication of this is that the best thing we can do for the well being of the environment is to turn to the Lord. The locusts had devastated the land itself, and the animals would be suffering as much as the people. They would both benefit from God’s salvation. The crops would yield their harvest.