Song of Songs
Pesach is very much connected with the גאולה, Redemption. Just as we were redeemed from Egypt in the month of Nissan, our future Redemption will also take place in Nissan.
For this reason, it is the Minhag among Ashkenazi Jews, to read שיר השירים, Song of Songs, on Pesach.
It was Rabbi Akiva who convinced the other Tannaim of the specialness of this work by King Solomon, that he called it, קודש הקדשים, the holy of holies of the books of Tanach.
The analogy is made between the true love of a man and his wife, and Hashem and the Jewish people. The loving relationship between a husband and wife, based on mutual values, love of G-d and the Torah, is intended to be the highest connection between two individuals.
Similarly, the special bond between Hashem and the Jewish people, is loftier than any other nation on earth. The ultimate connection will take place when Mashiach comes and all the earth acknowledges Hashem as the One and only true G-d.
Sefirat Haomer: Yesterday was four. Shabbat Shalom and Chag Sameach.