The Chida writes that one must be concerned about fulfilling the mitzva of Matnos Kehuna because they answered R’ Yaakov of Marvege from heaven that it is a sin not to do it.
There were tzadikim who undertook certain spiritual preparations and were able to ask specific questions prior to going to sleep and then receive answers in their dreams from Eliyahu or Malachim. This method is known as sheilas chalom, dream question. A reference to this is found in וישאל שאול בה' ולא ענהו ה' גם בחלומות גם באורים גם בנביאים (Shmuel 1, 28:6), Shaul inquired of Hashem but Hashem didn’t answer him; neither in a dream, nor through the Urim V’tumim nor through the prophets. (See the Redak and the Ralbag there. See also the Ibn Ezra to Shemos 14:19 and Rabbeinu Bachaye to Devarim 29:28.)
The Vilna Gaon would slaughter a calf and give the foreleg, jaw with the tongue and maw to the kohen and say a shehechiyanu. When he gave the Matnos Kehuna to the kohen he instructed him to carry it publicly in order to publicize it.
The Chassam Sofer writes, “I was accustomed to give Matnos Kehuna — foreleg, jaw and the maw — to my brother-in-law who was married to a kohenes. Also, each Yom Tov I would shecht an animal and separate Matnos Kehuna from it. I would do the same with Reishis Hagaiz, the first of the flock’s shearing.”
