The Torah was edited with great precision. This is the idea behind the notion that "there is no chronological order to the Torah". Items are placed were they can teach the greatest messages—form can be as important as substance.
Our Sages equated farming with faith. Only a man of faith could put in months of backbreaking labour, knowing full well that all his efforts could go for naught with a few days of bad weather. It is the farmer who, more than others, realizes that his success is truly in the hands of G-d. This realization is meant to spur the farmer to “hearken to the commandments which I am prescribing today” in order to have “rains in your land at the proper time”.