Our Gemara on Amud Aleph tells us that there is an obligation to make sure that Pesach falls out during the spring. Since the Jewish calendar follows the lunar months, a Jewish year is approximately 354 days. In order to keep the Jewish year aligned with seasons, there must be 7 leap years in every 19 Jewish years, adding on a second month of Adar.
Elsewhere in Psychology of the Daf (Yoma 65) we discussed the significance of the Jewish Calendar and its integration of both solar and lunar cycles. Today I would like to offer an additional insight based on Rav Moshe Amiel (דרשות אל עמי חגים וזמנים שונים כב).
God’s Providence in the world can be observed via phenomena leading to a root cause. For example, we see a world that is created and can conclude there is a creator. The experience of Pesach, the foundation of Jewish belief, begins in the Springtime to emphasize the idea of the root cause. The harvest may come in the fall (Succos time), but the real root cause is the planting in the Spring (Pesach time.) Avraham set himself apart from his contemporaries by not worshiping the phenomena, such as the Sun and the Moon, but rather the root cause, the Creator.
The Gemara later on 8a notes that the Jewish year begins in Nissan only for Jewish kings. However, we count from Tishrei for secular kings. This too emphasizes the point that the Jewish perspective looks for the root cause and not merely the superficial phenomena.
Translations Courtesy of Sefaria, (except when, sometimes, I disagree with the translation .)