Your threshing shall reach unto the vintage, i.e. you shall have so plentiful a harvest, that you shall not be able to thresh out your corn in a little time, but that work will last till the vintage.
Related Commentaries of Leviticus 26:5
Leviticus 26:5
5 And your threshing shall reach unto the vintage, and the vintage shall reach unto the sowing time: and ye shall eat your bread to the full, and dwell in your land safely.