Why do we say If I forget you, Jerusalem, etc., at a wedding

Shalom uvrakhah,

The custom is for the groom to break a glass under the chuppah, and the reason is so that the joy not become uncontrolled, as it is stated (Psalms 2:11), Serve Hashem with joy and rejoice with trembling (see Berakhot 31a, Tosafot there, s.v. Aytivi, and Sefer HaRokeach, siman 353).

And since it is common that people turn the custom of breaking the glass into levity and frivolity, when the groom forcefully stomps on the glass to break it, and everyone fills their mouths with laughter and cries of Mazal tov, this is exactly the opposite of the intent of this fine custom, which is meant to express sorrow for the destruction of our holy and glorious Temple, and to place Jerusalem at the head of our joy. Therefore, in many places it has become customary for the officiating rabbi to instruct the groom to say before breaking the glass, If I forget you, Jerusalem, let my right hand forget, in order to make known that this is a remembrance of the destruction of the Temple, and then, little by little, the crowd will understand the background to the breaking of the glass and will not turn it into mockery and derision (see at length in Yabia Omer, vol. 4, Even HaEzer, siman 9).

With blessing,

Hillel Meirs