Truth

The word Samayach (שמח), happy, can be spelled out as: Shin, Mem, Ches (ש’ין מ’ם ח’ית). The inner letters equal 510. This spells Yashar (ישר). This is to hint that true joy comes from honesty.

The Chasson and Kallah have established their marriage on honesty and trust, may Hashem grant them the ability to always be Samayach each other!