Category A: Chosen Priests
For the LORD your God has chosen [Aaron] out of all your tribes to stand to minister in the name of the LORD, him and his sons forever. (Deuteronomy 18:5)
Did I not choose him out of all the tribes of Israel to be My priest, to offer upon My altar, to burn incense, and to wear an ephod before Me? (1 Samuel 2:28a)
In this category, the first element of God's choice (the identification of the chosen), was Aaron and his sons. As we saw in the story of Korah, this was a clearly defined choice of God, and deliberate. It was clearly defined in the sense that there was no mistaking God's intention of who was chosen. It was deliberate in the sense that no other family could replace the family of Aaron, as Korah so painfully discovered. It was a choice in the sense that Aaron's family was selected from among the myriads of families in the nation.
The second element, the purpose for which they were chosen, was identified as the role and function of the priesthood. It was not that God chose Aaron's family for some greater level of blessing above everyone else (such as an increased portion of the promised land, or greater riches), but that God intended for Aaron's family to fulfill the specific purpose of functioning as priests.
The third element, regarding the permanence of His choice, was clearly stated in the above verse, '...the LORD your God has chosen... ...him and his sons forever." In other words, as long as there was a priesthood in Israel, the priests would be of the family of Aaron.
The final element, a position of holiness, can easily be shown as true in this context. The priests were made holy unto the Lord, and He gave considerable instruction on how the holiness was to be established and maintained.