From Preface to Pesach 2 (#118) by Rabbi Avigdor Miller
Q: Why is the Torah interested that Pesach falls in the spring month when things are growing?
A: The Torah wants us to celebrate Pesach with a certain amount of physical gratitude, physical happiness.
Every yom tov has two names: we call Shavuos the "yom tov of the giving of the Torah," but it’s also called chag habikkurim, the holiday of the ripe fruits. How does that fit in? the answer is when you’re munching your ripe fruit it’s much easier to appreciate the giving of the Torah. That’s why when you make a siyum, when you complete a sefer of the Torah, you eat. What’s eating got to do with studying of the Torah? The answer is when you’re eating it’s easier to appreciate the spiritual things.
Torah wants us to celebrate Pesach with a certain amount of physical gratitude
And that’s why Sukkos is called chag ha’asif, the festival of the ingathering of the crops. Why mention crops? We’re talking about remembering sukkot that our forefathers made. The answer is when you have the harvest secure in your bins, and your storehouses are bursting with wheat, with barley, with rye and you got big barrels full of wine and you have oil and the place is all set for a winter of many good times, many good meals then it’s easier to celebrate a yom tov.
That’s why Pesach comes in the aviv (spring) that’s when the grain is already ready for reaping: for the purpose of making us more grateful and more capable of appreciating.