Why do we read Shir HaShirim on Pesach? The Sfas Emes teaches that there is a close connection between Shir HaShirim and Pesach.
Shir HaShirim is a love song. Shir HaShirim uses the love between a man and a woman as a metaphor for how to love God. Essentially, Shir HaShirim teaches us that every aspect of this world is only an allegory to help us understand the love that we need to have for God.
This is a difficult level to attain. It is particularly difficult to view this world as a metaphor when it seems so real to us because we are so attached to it, to fulfill our physical desires and needs.
On Pesach, though, this task becomes easier. On Pesach God showed us that His divine will works through nature. God directly involved Himself in rescuing us from
Pesach is therefore called זמן חירותנו/the time of our freedom. Time represents the natural world because time exists only in the physical world. On Pesach we can free ourselves from our attachment to the physical and learn God’s will from nature.
Therefore, the message of Shir HaShirim and that of Pesach complement each other. Shir HaShirim teaches us to view the world as a metaphor from which we can learn how best to serve God. Pesach is the best time to do this because Pesach is the “time of our freedom”. It is when God revealed to us His providence in the physical world.
This is why Shir HaShirim is read specifically on Pesach.