"This sin of the young men was very great in the Lord's sight, for they were treating the Lord's offering with contempt." NIV translation
The actions of the sons of Eli demonstrated that their hearts were not right with God. This reminds us that our faith does not depend on our location but on the state of our hearts. When a person's heart is right, their actions will follow. When their heart is not right, it does not matter how many times you attend a place of worship. Eli's sons were raised at the Tabernacle and were there daily yet they were very far from God.
"But Samuel was ministering before the Lord - a boy wearing a linen ephod." NIV translation
The linen ephod was what was prescribed by God to be worn by the men that were serving Him. Samuel was wearing the garment as prescribed and it reminds us that obedience is an act of love.
This is a big contrast between Samuel and Eli's sons. They were concerned with serving their own flesh while he was concerned with the things of God.
It is also a good way of determining where we are at in our walk with the Lord. If we, like Eli's sons are busy chasing after the things of this world, we need to examine our hearts.
This is what Jesus was talking about when He told His disciples to store up treasures in heaven. He went on to say that no one can serve two masters (see Matthew 6).
"Each year his mother made him a little robe and took it to him when she went up with her husband to offer the annual sacrifice." NIV translation
We see that Samuel was given a robe by his mother each year but he wore the linen ephod when he was ministering in the Tabernacle. We also see that, even though she had given what we would consider the ultimate sacrifice (her son), Hannah continued to go to Shiloh each year. That is a reminder to us that our service to our Lord and Savior is not a one time thing or even a weekly thing. Either Jesus is our Master and we are continually serving Him or we are are slaves to the world and the flesh.