The period between Passover/Easter and the Feast of Weeks, in ancient times, marked the beginning and end of the grain harvesting season, starting with the early-ripening barley, and ending with the wheat.  For the ancient agriculturalists, however, this seven-week period was fraught with anxiety.  The weather at the end of winter and beginning of spring is highly unpredictable.  Even now, in late April, I never know if the following day I'll be bundling up in a sweater or out in shorts and a t-shirt.  Farmers in ancient times - and even the farmers of today - can expect anything from rain and hail to scorching heat waves - and any of these extreme weather conditions could ruin his crop. 

But in ancient times, for months, the farmer had toiled to plow the hard earth - praying for an early rain to soften the soil, sowed the seeds and then prayed for the later rains that would water his crops. And if everything went well, and the grain grew to maturity, the prospect of losing it all just before the harvest was maddening.  With this in mind, we can truly understand the importance to the ancient Israelites of the promise of the covenant: 

"It shall come about, if you listen obediently to my commandments which I am commanding you today, to love the LORD your God and to serve Him with all your heart and all your soul, that He will give the rain for your land in its season, the early and late rain, that you may gather in your grain and your new wine and your oil."  Deuteronomy 11:13-14

Note:  References in certain translations of the Bible to corn, actually refer to grain.  Corn was not an agricultural product in ancient Israel.