The ladder is a person

The Berditchever Rav, in Kedushas Levi, reads Yaakov's dream as a picture of every person who serves Hashem. A ladder set on the earth is a human being standing in this world; its top reaching the heavens is his avodah (service of Hashem), which reaches above. The angels of Hashem rise and descend on it, which he reads as through him: a person's deeds lift the upper worlds, and the opposite can bring them down. At the beginning, the Rebbe says, a person is fired up by the thought that his deeds move all the worlds, and this strengthens him. He reads the word vayachalom (he dreamed) as related to strengthening. Later, once he is firm in his service, he no longer thinks about himself at all, only about Hashem, and then "Hashem stood over him": he becomes a chariot (merkavah) for the Shechinah.