1)
What is the connection between harvest, summer and salvation?
1.
Rashi: They expected help from Egypt, but it did not come. They thought that they are busy harvesting, and afterwards they will come to help. The harvest, in Iyar, passed, and Kayitz in Tamuz, and they did not come.
2.
Radak: Harvest is when man is saved from scarcity; he is happy when harvest comes, like it says "k'Simchah b'Katzir" (Yeshayah 9:2). The entire summer, a man is happy with summer fruits. This is a parable - the times when we expected to be saved, they passed, and we were not saved.
3.
Malbim: The 10 tribes say, we have waited a long time for salvation!