Rebbe Nachman says, Yom Tov stands on the street corner and screams out to the world, “Please know that G-d is leading the world, that there is no nature!” He says that you have to listen with your ears and your heart very closely to hear this screaming. The more you hear the Yom Tov yelling out that G-d is leading the world, the more you feel the joy of Yom Tov. G-d forbid, if you are not so happy on Yom Tov, that means you didn’t hear it calling.
How do you get your ears to hear Yom Tov calling? Before Pesach you must give charity, you have to give to the poor. You train your ears by hearing the cries of those in need. Then your ears become refined, and on Yom Tov you can hear G-d telling you, “Know, there is only one G-d.” But if your ears are not open to the crying of the poor, then your ears are deaf and you cannot hear G-d calling either.