The love and connection between us make it possible for us to stand together before God. Therefore, before praying, one needs to accept upon himself love for every Jew, so that his prayer can ascend to God.

Before one says his prayers in the synagogue…he must accept upon himself the mitzva of “You shall love your fellow as yourself,” and he must have the intention of loving every Jew as he loves himself. For this is how his prayer will ascend: Together with all the prayers of Israel, and in this way it will be able to rise up and produce a good outcome. (Rabbi Yitzĥak Luria (Arizal), Sha’ar HaKavanot, Derushei Birkot HaShaĥar)