What does 1 Samuel 2:28 mean?

A man of God, an unnamed prophet, has come to the priest of the Lord's sanctuary, Eli, at Shiloh (1 Samuel 2:27). Through this man, the Lord has asked Eli to remember that his ancestors were freed from slavery by God's miraculous power. The use of questions, instead of statements, is meant as a challenge—almost daring Eli to deny this was the case. Eli was a direct descendant of Aaron, the first high priest of Israel and Moses' brother (Exodus 29:44).

Now God applies the same tactic while referring to Aaron, chosen out of all the tribes of Israel, to be His priest. The Lord then mentions several of the duties of the priest. The priest is the one permitted to go up to the Lord's altar to offer the sacrifices (Leviticus 1:9). The priest burned incense before the Lord on a special altar (Exodus 30:7). The burning of the incense was meant, in part, to create a kind of cloud covering for the priest's protection (Leviticus 16:13). Finally, the Lord mentions that Aaron was chosen as the high priest to wear the official priestly ephod garment in His presence (Leviticus 8:7). This official ephod is described in Exodus 28:6–30 and is different from the more common priestly ephods, such as the one young Samuel wore (1 Samuel 2:18).

Finally, the Lord says to Eli that He gave to Eli's father, meaning Aaron and his descendants, all the offerings by fire from Israel's worshipers. By this, the Lord means that the priests were given a portion of the offerings for their own food, aside from those that were burned up completely (Leviticus 6:14–18; 7:1–38).