The Esrog - Alone

It takes a conscious effort to connect the Esrog to the other three species because oftentimes the Tzaddikim -righteous (who are symbolized by the Esrog) have a tendency to look upon the wicked with a superficial glance and distance and separate from them. They must make sure that they do not separate from the other three species and to join the Esrog with the Lulav and Aravah (which represent those less righteous) so they are literally one.
It is the righteous who are most likely to err when it comes to unity. The forces of evil make every effort to cause them to err as they know that if the righteous would make peace with everyone else and feel unified with the rest of the Jewish Nation, as symbolized by the Lulav, then the Redemption would come immediately. The Yetzer Hora makes every effort to separate the Esrog from the other species and to instill within them thoughts of separation, filled with hubris. G-d forbid that people should fall into this trap because within lies the secret of our Redemption.
א"ת קמ"א