Samuel is given spiritually and physically to the Lord.
Samuel, according to His age, rendered such practical help as would be required in assisting the high priest. God was shaping and developing him to succeed Eli whether Eli knew it or not.
Or to train others to minister to the Lord.
Eli's sons, because of their wickedness, would not be the chosen of God to follow on after their father. They were "corrupt; they did not know the Lord." (1 Samuel 2:12 NKJV). They had not entered into fellowship with the Lord, nor acknowledged His claims on
their lives. (1 Samuel 2:12-17 ).
New Testament ministry must not be motivated by lust for power or greed for possessions.
Eli knew about his sons' evil but did not stop them - he let them bring discredit upon him, disdain upon the worship and debasement to the people, and to themselves damnation. To be the easy-going father and not confront serious problems is sin, and can bring painful
consequences.
Evidenced by the increased size of clothing brought annually by his loving mother. But his was growth in spirit, soul and body (1 Samuel 2:18-21 ). Note how blessed Hannah was with sons and daughters (1 Samuel 2:21 ).
In terrible contrast Eli's sons grew in wickedness (1 Samuel 2:22-23 ).
Aged, feeble Eli remonstrates too late (1 Samuel 2:22-25 ).
Too late - such was the hardness of their rebellious hearts. Like Pharaoh, nothing could now avert the punishment of sons who would not heed.
The prophet announced:
It would, of course, refer to Samuel's succession to Eli himself - but also to Zadok who was anointed high priest in place of Abiathar, the last descendant of Eli's line. (See 1 Kings 2:26-27 ). God wants faithful people to fulfil his work faithfully.
1.3. PRIESTLY UNFAITHFULNESS REPLACED BY FAITHFUL (1
Samuel 2:11-36)
1.3.1. WITHOUT GRUDGING OR REGRET
1 Samuel 2:11 "... And the child did minister unto the LORD before Eli the priest."
1.3.2. GREAT PRIVILEGE TO BE TRAINED
2 Timothy 1:5 "when I call to remembrance the genuine faith that is in you, which dwelt first in your grandmother Lois and your mother Eunice,
and I am persuaded is in you also."
1 Samuel 2:17 "Wherefore the sin of the young men was very great before the LORD: for men abhorred the offering of the LORD."
"The sons of Eli were guilty of taking more of the sacrifice than their allotted portion (Leviticus 7:34 ), of taking the meat before the fat had been burned as a sacrifice to God (Leviticus 3:3, 5 ), and of
generally despising the offering of the Lord. (1 Samuel 2:17 )." Ryrie
1 Peter 5:2,3 "Shepherd the flock of God which is among you, serving as overseers, not by compulsion but willingly, not for dishonest gain but
eagerly;3 nor as being lords over those entrusted to you, but being examples to the flock;"
1.3.3. SAMUEL GREW PHYSICALLY
1 Samuel 2:21 "And the LORD visited Hannah, so that she conceived, and bare three sons and two daughters. And the child Samuel grew before the
LORD."
1 Samuel 2:23 "... for I hear of your evil dealings by all this people."
1 Samuel 2:25 "... But if a man sins against the Lord, who will intercede for him?" Nevertheless they did not heed the voice of their father, because
the Lord desired to kill them."
1.3.4. JUDGMENT IS PROPHESIED OVER ELI'S HOUSE (1 Samuel 2:27-36)
1 Samuel 2:34 "And this shall be a sign unto thee, that shall come upon thy two sons, on Hophni and Phinehas; in one day they shall die both of
them."

God Is Just Leaders cannot get away with displeasing God, or failing in allowing sin - they are accountable and will be judged. 
God Is Faithful God disciplines leaders but never leaves His people leaderless.
1 Samuel 2:35 "And I will raise me up a faithful priest, that shall do according to that which is in mine heart and in my mind: ..."
1.3.5. THE FULFILMENT OF THE PROPHECY