Charles Spurgeon Commentary 1 Samuel 2:28-30

"and did I choose him out of all the tribes of Israel to be my priest, to go up unto mine altar, to burn incense, to wear an ephod before me? and did I give unto the house of thy father all the offerings of the children of Israel made by fire? Wherefore kick ye at my sacrifice and at mine offering, which I have commanded in [my] habitation, and honorest thy sons above me, to make yourselves fat with the chiefest of all the offerings of Israel my people? Therefore Jehovah, the God of Israel, saith, I said indeed that thy house, and the house of thy father, should walk before me for ever: but now Jehovah saith, Be it far from me; for them that honor me I will honor, and they that despise me shall be lightly esteemed." — 1 Samuel 2:28-30 (ASV)

Out of all the tribes of Israel to be my priest, to offer upon mine altar, to burn incense, to wear an ephod before me? and did I give unto the house of thy father all the offerings made by fire of the children of Israel? Wherefore kick ye at my sacrifice and at mine offering, which I have commanded in my habitation; and honourest thy sons above me, to make yourselves fat with the chiefest of all the offerings of Israel my people? Wherefore the Lord God of Israel saith, I said indeed that thy house, and the house of thy father, should walk before me for ever:

There was a condition attached to that promise—a condition implied, if not expressly stated.