Looking ever more closely to the writtings of Joel it would appear that Joel is expressing the devouring of the land including the trees (men)to where there is only stubble in the vineyard (Israel)which is left from the army of locust, palmerworm, cankerworm and caterpiller (false prophets & teachers). The land laid a waste land, but God said a day of drought will come and dry up the rivers of waters (truth) and fire will devour the pastures of the wilderness and all the trees of the field. That they should gather the asssembly together and cry unto the Lord.
This chapter seems to continue with that thought and say that day of the Lord is nigh at hand. A fire will come and devour before them and behind them. Given that fire is a way of purification and in verse 5 it descibes the army that is to come upon them shall devour the stubble that which was left by the Locust.
Neither this army of God is shall fall upon the sword (word of God) shall be wounded. For they shall be a people set in battle array. The Lord calls the people of Israel to turn again their hearts unto him and that he would show great mercy and be anger, but only if they call for an assembly to repent and be sancified.
3A fire devoureth before them; and behind them a flame burneth: the land is as the garden of Eden before them, and behind them a desolate wilderness; yea, and nothing shall escape them.
4The appearance of them is as the appearance of horses; and as horsemen, so shall they run.
5Like the noise of chariots on the tops of mountains shall they leap, like the noise of a flame of fire that devoureth the stubble, as a strong people set in battle array.
That then will God be jealous for his land and pity for his people, if they return to him that he would restore the days of the locust and send corn, wine and oil that you shall be sancified. That God would remove the northren army and bring you back into your land and pour out the former and latter rain in the first month of the season.(Holy Spirit) Thus restoring the years that the locust hath eaten, my great army that God has sent unto them. Thus the army of God is the harvest of the earth that wheat and barley in one seasonal month.
Is a continuation of those days in which God would restore Judah and Jersualem in gathering those that are scatter among the nations. It speaks of precaliming war among the nations that all men might draw near, even the farmer is called into battle beating his plowshares into swords to sow in the field no more, but to being the harvest. Put in the sickle for the havest is ripe. In that day the mounatin shall drop down with new wine and the hills shall flow with milk and a fountain out of the house of the Lord.
Seems to me that each chapter continues the same thoughts and descibes the same events which would be that the land was first laid waste by false prophets and teachers causing the people to sin. God would have them to call for a general assemby and repent and be sancified. In chapter 2 it relates in a way of an invasion by the army of God that will make clean and puriftied thereby clearing the land of stubble and weeds, leaving the ground as clean as possible for the tillage tools.
This leaves me to ask can we assume that the army of God (2:11) is an pagan nation that can't be wounded? Clearly this speaks of the army of God that speads the words of God as if it was 'fire' and as a 'sword' to make ready the land for it planting and harvesting of souls.