Simcha in Avodas Mitzva

Sefer Pisgomin Kadishin

Every Avodas Mitzva (service of commandment) and praise must be in complete Simcha (happiness), as we find in the Gemoroh (Brochos 30:1) we see with Abayei who would jest a lot and say I am placing Tefillin. And so, to Rav Bruna who would be joining Geuloh to Tefilloh, and it would be endless happiness from his mouth that whole day.

Rav Chaim Vital, Sharei Kedusha,2:4, Sefer Ohz Tischazeik