God planted a people to be called by His name. The people rejected God. After some period of time, God will restore the people of Israel to their original place. The latter rains represents Israel's restoration, God's blessings and God's use of the Israel. Israel's believed that just as the seasonal rains came to revive the earth, God's favor would come to revive his people.
Early rain starts the seed off.
Latter heavy rain gave them growth. God supplies the rain. He will cause the Jewish people to be saved. He will use the Jewish people to save other people. As the fruit matures so will the tares.