+ Positive Mitzvah
The Kohanim bless the Jews
“So shall you bless the children of Israel…” Bemidbar 6: 23
---“May God bless you and safeguard you’’6:24 (regarding physical possessions)
---“May God illuminate His countenance for you and be gracious to you ‘’ 6:25 (May he show you a glad face and give you grace/ also refers to Torah wisdom)
--- “May God lift His countenance to you and establish peace" 6:26 (withhold His anger and give you peace)
If a Kohen adds some other blessing he transgressors the negative commandment (-159) “you shall not add to it” Devarim 13:1:
If a Kohen did not go up at the time when the person leading the prayers call “Kohanim” he violates this positive commandment and three others
” So shall you bless” Bemidbar 6:23 (so that all of them shall hear) and
“Saying to them” (do not bless them in haste but with attention and wholeheartedness)
“Let them place My name” Bemidbar 6:27
They will bless using Gods name and He will agree with them. ref Rashi.
God told Abraham that He will bless those who bless you, so He also blesses the Kohanim in return. Chulin 49a.
In Israel these blessings are done daily and in the Diaspora reserved for the holidays.
This is applicable in all place at all times.