I had wondered about Nathaniels over the top response for years, it seemed out of place given what Jesus said. I read about the significance of fig trees in the Old Testament and understood the fig tree to be a symbol of Israel. A fig tree with figs was a symbol of prosperity and blessing and a fig tree without fruit was a symbol of judgement and curse.
Not long ago I was attempting to read Rabbi Maimonides' "guide to the perplexed," when I stumbled on the answer concerning Nathaniel.
According Maimonides if an Israelite wanted to express thanks for times of abundance or hope in difficult times one way would be to pray underneath a fig tree. Praying under a fig tree indicated complete trust in God and specifically God would "see him." When Jesus said "I saw you under the fig tree," it immediately completed Nathaniels reason for being under the fig tree in the first place.... To be seen as a faithful Israelite by God.