Honoring your children above Me

[2 Sam. 227] And there came a man of God unto Eli, and said unto him, Thus saith the LORD, Did I plainly appear unto the house of thy father, when they were in Egypt in Pharaoh's house?
Eli was chosen by G-d to be His priest, to serve as a mediator between G-d and His people; but in this calling Eli and his house failed. Consequently, words of judgment came upon them. Election, according to the O.T. is not for privilege but for responsibility. Failure to fulfill one’s responsibility makes one doubly accountable to G-d (Amos 3:2).
A man of G-d probably refers to a prophet. Samuel appears to be the natural successor; subsequently other members of Eli’s house have also been functioning in different locations – Ahijah (14:3) and Abithar (22:20). Eventually Abiathar was exiled, and thus Eli’s line came to an end. Zadok then became the head of the priestly order.
[28] And did I choose him 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?
House of your father is a reference to Levi, to the Aaronite line in particular. A promise by G-d cannot stand unless there is corresponding obedience because G-d deals with humans who possess free will.
[29] 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?
Eli exercises his responsibility as father in warning his children against their evil practices in the Temple. How he is charged for not restraining his sons.
Eli reproved his sons too gently, and did not threaten them as he should, and therefore G-d sent a prophet to him to reprove him sharply, and to threaten him, because, by his indulgence of them, he had strengthened their hands in their wickedness. If good men be wanting in their duty, and by their carelessness and remissness contribute any thing to the sin of sinners, they must expect both to hear of it and to smart for it.
His children did wickedly, and he connived at it, and thereby involved himself in the guilt; the indictment therefore runs against them all.
[30] 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: but now the LORD saith, Be it far from me; for them that honour me I will honour, and they that despise me shall be lightly esteemed.
The promise carried its own condition along with it: “They shall walk before me forever, that is, "they shall have the honor, provided they faithfully do the service." Walking before G-d is the great condition of the covenant, Genesis 17:1.
[31] Behold, the days come, that I will cut off thine arm, and the arm of thy father's house, that there shall not be an old man in thine house.
Eli’s posterity will be cut off. Israelites seem to have believed in some kind of an ongoing existence remembrance through their posterity, through male progeny. That is why they saw the need for the levirate marriage system, which covered the case of a man dying without issue. To have one’s posterity cut off was considered to be a great curse and a terrible misfortune. By the withdrawal of the high priesthood from Eleazar, the elder of Aaron's two sons (after Nadab and Abihu were destroyed, (Numbers 3:4), that dignity had been conferred on the family of Ithamar, to which Eli belonged, and now that his descendants had forfeited the honor, it was to be taken from them and restored to the elder branch.
To die in old age was a sign of G-d’s blessings in Israel, but to die prematurely was considered to be a curse. So much importance has always, in the East, been attached to old age, that it would be felt to be a great calamity, and sensibly, to lower the respectability of any family which could boast of few or no old men. The prediction of this prophet was fully confirmed by the afflictions, degradation, poverty, and many untimely deaths because he honored his sons above G-d.
The message is sent to Eli himself, because G-d would bring him to repentance and save him; not to his sons, whom he had determined to destroy. And it might have been a means of awakening him to do his duty at last, and so to have prevented the judgment, but we do not find it had any great effect upon him.
The distinguishing favors we have received from G-d, are great aggravations of sin, and will be remembered against us in the day of account, if we profane our crown and betray our trusts, Deuteronomy 32:6, 2 Sam. 12:7, 8.
[3:13] For I have told him that I will judge his house for ever for the iniquity which he knoweth; because his sons made themselves vile, and he restrained them not.

[1 Cor. 5:9] I wrote unto you in an epistle not to company with fornicators:
[10] Yet not altogether with the fornicators of this world, or with the covetous, or extortioners, or with idolaters; for then must ye needs go out of the world.
[11] But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
[12] For what have I to do to judge them also that are without? do not ye judge them that are within?
[13] But them that are without God judgeth. Therefore put away from among yourselves that wicked person.
He tells them that if any man called a brother, any one professing Christianity, and being a member of a Christian church, were a fornicator, or covetous, or an idolater, or a railer, that they should not keep company with him, nor so much as eat with such a one. They were to avoid all familiarity with him; they were to have no commerce with him; they were to have no commerce with him: but, that they might shame him, and bring him to repentance, must disclaim and shun him. Christians are to avoid the familiar conversation of fellow-Christians that are notoriously wicked, and under just censure for their flagitious practices. Such disgrace the Christian name. They may call themselves brethren in Christ, but they are not Christian brethren. They are only fit companions for the brethren in iniquity; and to such company they should be left, till they mend their ways and doings.
How he limits this advice. He does not forbid the Christians the like commerce with scandalously wicked heathens. He does not forbid their eating nor conversing with the fornicators of this world. They know no better. They profess no better. The idols they serve, and the worship they render to many of them, countenance such wickedness. "You must needs go out of the world if you will have no conversation with such men. Your Gentile neighbors are generally vicious and profane; and it is impossible, as long as you are in the world, and have any worldly business to do, but you must fall into their company. This cannot be wholly avoided." Note, Christians may and ought to testify more respect to loose worldlings than to loose Christians. This seems a paradox. Why should we shun the company of a profane or loose Christian, rather than that of a profane or loose heathen?
G-d can and will preserve them from contagion. Besides, they carry an antidote against the infection of their bad example, and are naturally upon their guard. They are apt to have a horror at their wicked practices. But the dread of sin wears off by familiar converse with wicked Christians. Our own safety and preservation are a reason of this difference. But, besides, heathens were such as Christians had nothing to do to judge and censure, and avoid upon a censure passed; for they are without, and must be left to G-d's judgment. But, as to members of the church, they are within, are professedly bound by the Laws and rules of Christianity, and not only liable to the judgment of G-d, but to the censures of those who are set over them, and the fellow-members of the same body, when they transgress those rules. Every Christian is bound to judge them unfit for communion and familiar converse. They are to be punished, by having this mark of disgrace put upon them, that they may be shamed, and, if possible, reclaimed thereby: and the more because the sins of such much more dishonor G-d than the sins of the openly wicked and profane can do. The church therefore is obliged to clear herself from all confederacy with them, or connivance at them, and to bear testimony against their wicked practices. Though the church has nothing to do with those without, it must endeavor to keep clear of the guilt and reproach of those within. Cast him out of your fellowship, and avoid his conversation.
Eli was not cast out of the body because of the sins of his children, he was the believer not his children, his curse was caused because he honored his children in his house above G-d, by his indulgence of them.