(1) Now Aaron’s sons Nadab and Abihu each took his fire pan, put fire in it, and laid incense on it; and they offered before יהוה (Adonai) strange fire, which had not been enjoined upon them. (2) And fire came forth from יהוה and consumed them; thus they died at the instance of יהוה. (3) Then Moses said to Aaron, “This is what יהוה meant by saying: Through those near to Me I show Myself holy, And gain glory before all the people.” And Aaron was silent. (4) Moses called Mishael and Elzaphan, sons of Uzziel the uncle of Aaron, and said to them, “Come forward and carry your kinsmen away from the front of the sanctuary to a place outside the camp.” (5) They came forward and carried them out of the camp by their tunics, as Moses had ordered. (6) And Moses said to Aaron and to his sons Eleazar and Ithamar, “Do not bare your heads and do not rend your clothes, lest you die and anger strike the whole community. But your kin, all the house of Israel, shall bewail the burning that יהוה has wrought. (7) And so do not go outside the entrance of the Tent of Meeting, lest you die, for יהוה’s anointing oil is upon you.” And they did as Moses had bidden.
WHICH G-D HAD NOT COMMANDED THEM. They (Nadav & Abihu) acted on their own and were not commanded to burn incense and certainly not to employ a strange fire.
[כג]...היה אהרן עומד ותוהא, אומר "אוי לי, כך עבירה בידי וביד בני שכך הגעתני". נכנס משה אצלו והיה מפייסו. אמר לו: אהרן אחי, מסיני נאמר לי "עתיד אני לקדש את הבית הזה – באדם גדול אני מקדשו". הייתי סבור או בי או בך בית מתקדש. עכשיו נמצאו בניך גדולים ממני וממך שבהם הבית נתקדש. כיון ששמע אהרן כך – צדק עליו את הדין ושתק שנאמר "וידם אהרן".ולמודים צדיקים שמצדיקים עליהם את הדין. אברהם צדק עליו את הדין שנאמר (בראשית יח, כז) "ואנכי עפר ואפר" עקב צדק עליו את הדין שנאמר (בראשית לב, יא) "קטנתי מכל החסדים ומכל האמת אשר עשית את עבדך"
23)...Aaron stood in astonishment, saying: Woe unto me! There must be transgression in me and in my sons that such has befallen me! Thereupon Moses entered and comforted him, saying: "Aaron, my brother, from Sinai it was revealed to me: 'I (Adonai) am destined to consecrate this house (the mishkan) — I will do so with a great man.' I thought to myself that the house will be consecrated either through me or through you. We find now that your two sons are greater than both of us, the house having been consecrated through them. When Aaron heard this, he vindicated G d's judgment upon him and he was silent, as it is written (Vayikra 10:3): "And Aaron kept his peace." And the righteous are wont to vindicate G d's judgment upon them. Abraham did so, viz. (Bereshith 18:27): "… and I am dust and ashes." Jacob did so, viz. (Bereshith 32:11): "I am too small for all of the lovingkindness and for all of the truth that You have conferred upon Your servant."
(א) דיני גלוח וסריקה באבל. ובו ז' סעיפים:
אבל אסור לגלח שערו אחד שער ראשו ואחד שער זקנו ואחד כל שער שבו ואפי' של בית הסתרים כל ל' יום ושער של השפה ומהצדדים כל שמעכב את האכילה תוך ז' אסור אחר שבעה מותר:
(1) A mourner is forbidden to cut their hair, both the hair of their head as well as the hair of their beard, or any hair that they have [on their body], even that of the secret parts, — for the entire thirty days. [As to] the hair of the upper lip and that which [droops] on the sides, — [the law is that] whatsoever causes a hindrance in partaking of food, is forbidden [to be trimmed] during the seven [days of mourning: shiva/siete(1)] and permitted after the seven [days of mourning].
(1)http://jewishstudies.washington.edu/omeka/exhibits/show/sephardic-life-cycles/meldado-memorial-sacred-space
(א) אבל אסור בכל מיני שמחה. ובו ג' סעיפים:
אבל אסור בשמחה לפיכך לא יקח תינוק בחיקו כל שבעה שמא יבא לידי שחוק:
(1) A mourner is forbidden joyous entertainment. Therefore, he should not take an infant in his arms, lest he be amused [thereby].
Although sheloshim (pronounced shlo-SHEEM, and also spelled shloshim) is a period of mourning, it is far less intense than shiva. The mourners resume normal social and professional duties but are still restricted in certain ways...
Another restriction observed for 30 days is not attending social events or even religious celebrations (Yoreh Deah, 391:1). However, a mourner may attend the ceremony itself, such as a circumcision as long as he does not stay for the festive meal that follows. Wearing new clothes during this period of time is also considered inappropriate...
This 30-day period eases the mourner back into normal routines by allowing the resumption of many but not all of one’s regular patterns of social behavior. At the conclusion of the 30 days, a sheloshim memorial service is often held, at which time various Jewish texts are taught in memory of the deceased.
Unless the bereaved is mourning a parent, the end of sheloshim marks the end of the mourning period. Although many people believe and even behave otherwise, after sheloshim the Mourner’s Kaddish is no longer traditionally recited for a spouse, sibling, or child. All mourning restrictions are lifted.
Excerpted from MyJewishLearning here: https://www.myjewishlearning.com/article/sheloshim-the-first-30-days-of-mourning/