Why do Jews hold the bride and groom up on chairs while dancing at orthodox weddings?

Answer

The guests are obligated to make the bride and groom joyful during their wedding (source: Talmud Brachot 6b).

In the Talmudic era they enlivened the wedding ceremonies in various ways. One of them was the dancing with the bride on the shoulder - (source: Talmud Ketubbot 17a).

If this pertains to you, Mazal Tov!