Only priests from the tribe of Levi, specifically descendants of Aaron, were authorized to perform the sacrificial rituals at the tabernacle/temple altar (Leviticus 1:5–8; Numbers 18:1–7). Any ritually clean Israelite could bring sacrifices to the temple, such as burnt offerings, peace offerings, or sin offerings, but they were not allowed to perform the sacrificial rites themselves. They would present their offering to the priests, who then carried out the ritual (Leviticus 1:2–3; Deuteronomy 12:27). In light of this reality, why was David, a man from the tribe of Judah, allowed to bring sacrifices? While it is possible that David simply organized the sacrifices and directed the Levites, if we assume that he did the actual rituals, then possibly he was permitted to do so because he had gained a priestly status. Psalm 110:4 hints at the fact that the descendant of David will be a priest in the order of Melchizedek. David may have acquired this status himself following his conquest of Jerusalem (see Genesis 14:18; Hebrews 7:1).
17 And they brought in the ark of the LORD and set it in its place, inside the tent that David had pitched for it. And David offered burnt offerings and peace offerings before the LORD.