Therefore I swear to the house of Eli that the iniquity of Eli’s house shall not be atoned for by sacrifice or offering forever.”
God did not come to flatter Samuel with tales of his own greatness, but to send him on an errand to another, far better use for a young man. This hard message about Eli's house would teach Samuel much later when his own sons turned wayward, not as bad as Eli's but not what they should have been.
AI summary
Commenting on 1 Samuel 3:11-18
And therefore I have sworn unto the house of Eli,.... Either had done this before, which was signified to him by the man of God, or did swear now for the confirmation of his threatenings, and to assure the certain performance of them: that the iniquity of Eli's house shall not be purged with sacrifice nor offering for ever: not even typically, which was all...
And therefore I have sworn unto the house of Eli, that the iniquity of Eli's house shall not be purged with sacrifice nor offering for ever. (i) Meaning that his posterity would never enjoy the chief priests office.