Ḥasidic mystical theology, combined with the ḥasidic tendency to invest minor details of custom with religious significance, led Ḥasidim to view ritual objects not invested with sanctity by halakhah—kiddush cups, seder plates, the decorations on the collars of prayer shawls, and so forth—as imbued with kabbalistic symbolism. Ḥasidic craftsmen then began to make these items with this symbolism in mind. In an interview with Alan Brill, Batsheva Goldman-Ida, the author of a recent book on this subject, explains:
The reason behind this radical move of investing objects with holiness is rooted in a general ḥasidic approach of “worship through the mundane.” This approach was very much part of early Ḥasidism and is generally attributed to [the movement’s founder], the Baal Shem Tov. . . .
The most important [style of] kiddush cup is the epl-bekher, or apple-shaped cup, whose form was designed by the Maggid of Mezrich [Rabbi Dov Ber, an early ḥasidic leader, ca. 1700-1772], according to tradition. The apple-form is symbolic of the Sh’khinah [or divine presence], as the “rose among thorns” which is “surrounded by five petals” as described in the opening pages of the Zohar . . .
The Ḥasid is required to hold the cup upright in his right hand—which represents the sfirah (emanation) of compassion—with all five fingers. . . . The apple-shaped cup is engraved with a winding chain with generally three leaves and a trefoil base. Over time, the petals underneath the cup were increased to thirteen, corresponding to the thirteen attributes of divine mercy, or to 26, corresponding to the numerical value of the Tetragrammaton. The finial at the top is sometimes in the form of an olive and other times in the form of a dove with outspread wings, both representing the “assembly of Israel,” [a kabbalistic term of art for the divine presence].
Read more on Book of Doctrines and Opinions: https://kavvanah.wordpress.com/2018/07/01/interview-with-batsheva-goldman-ida-hasidic-art-the-kabbalah/