And therefore I have sworn to the house of Eli that the iniquity of Eli’s house shall not be atoned for by sacrifice or offering forever. (1 Sam 3:14)
We know that Eli's two sons, though priests of the Lord, were exceedingly wicked and deserved to die. However, based on this verse, God appears to have been merciful and actually allowed their iniquity, for a long time, to be atoned for by sacrifices and offerings. God did not destroy them right away, though He desired to kill them. In fact, God warned Eli about his sons twice—once through a man of God (2:27-36) and another time through the boy Samuel (3:11-18).
When God spoke through Samuel, He included the word “forever,” implying that their sacrifices and offerings would soon be of no effect. In other words, God would no longer endure their sins. For while they sacrificed, they did not remove the very iniquities from their lives.
Ever since Jesus the High Priest sacrificed Himself for our sins once and for all (Heb 7:26-27), the sacrifice of animals is no longer needed. Instead, today we offer our prayers to God for forgiveness of our sins (Ps 141:2, Isa 56:7, Rev 5:8). So, what if we re-worded the above verse to apply to ourselves? And therefore I have sworn that your iniquity shall not be atoned for by prayers forever. This means that though God may be merciful and forgive our sins when we pray, perhaps this will not last forever, especially if we do not remove the very same iniquities from our lives.
Have we fallen into any traps of the lust of the flesh, the lust of the eyes, or the pride of life? And do we find ourselves always repenting to God but unable to change and remove these iniquities from our lives? If so, then let us remind ourselves that we should make an honest determination to change and rely on God for the strength and power to do so. Only then will our prayers be effective and heard by God.