Poole on 1 Samuel 2:18: Samuel vis a vis Eli's Sons

Verse 18:[1] (1 Sam. 2:11) But Samuel ministered before the LORD, being a child, (Ex. 28:4; 2 Sam. 6:14) girded with a linen ephod.

[Samuel was ministering before the face of the Lord] This is said, 1. Because he was ministering in the tabernacle. 2. At the nod, or command, of the Lord (Mendoza). 3. Because he was discharging his office without fault (Vatablus). He was ministering most perfectly, and with singular purity and sincerity of heart; as one that would strive to please divine, not human, eyes. It is a Hebraism, whereby what things are said to be done before the Lord are said to be done with the greatest perfection. See 2 Chronicles 26:4; Isaiah 53:2; Matthew 6:2-4 (Mendoza). This ministry was to study the Divine Law, to sing with the mouth, and to play on instruments of music (Munster).

Ministered, that is, performed his ministration carefully and faithfully, not corrupting nor abusing it, as Eli’s sons did. Before the Lord; in God’s tabernacle; or as in God’s presence, sincerely and regularly, with God’s approbation. Compare Genesis 17:1; 2 Chronicles 26:4.

[Girded with a linen ephod (thus Pagnine, Tigurinus), אֵפ֥וֹד בָּֽד׃] An ephod of linen (Montanus), or of flax (Jonathan, Syriac); a mantle (cloak [Arabic]) of linen (Junius and Tremellius). An ephod was a sort of garment, wherewith the Levities, drawing near to the worship of God, were dressed (Munster). Moreover, it was not lawful to wear these linen garments outside the Sanctuary. Neither the Levites, nor the very priests, outside of the Temple had any garment peculiar, and diverse from the common, as Josephus testifies in his Jewish Wars 6:6 (Sanchez). Moreover, the Ephod was twofold, 1. Sacerdotal, or rather Pontifical, concerning which Exodus 28:6. 2. The other common to the lesser priests, Levites, and even the laity, 2 Samuel 6:14 (Mendoza, similarly Sanchez). Wherefore this garment does not appear to have been sacred, since Samuel was clothed in it, before he had come to the age that he might be able to be consecrated as a Levite. See Numbers 8:6, 24 (Sanchez). An ephod was a sort of garment that covers the shoulders, and surrounds the chest; and, if we have regard to its use, it is sacred and religious; but, if we have regard to the persons that were wearing it, it was either Ecclesiastical, wherewith the High Priests, Priests, and Levites were clothed: or Political, wherewith Laymen were clothed (Menochius). Add that Samuel had been consecrated to God by a special vow[2] (Sanchez). Procopius and Theodoret think that this Ephod was sacerdotal, and was bestowed by Eli upon Samuel by special right: because of the admirable grace of God flourishing in him (Serarius). An Ephod was a very short garment, of which those that were ministering to the Lord were making use; not altogether dissimilar to the superhumeral of the high priest; but yet not entirely like it (Vatablus)

A linen ephod; a garment used in God’s service, and allowed not only to the inferior priests and Levites, but also to eminent persons of the people, as 2 Samuel 6:14, and therefore to Samuel, who, though no Levite, was a Nazarite, and that from his birth.

[1] Hebrew: וּשְׁמוּאֵ֕ל מְשָׁרֵ֖ת אֶת־פְּנֵ֣י יְהוָ֑ה נַ֕עַר חָג֖וּר אֵפ֥וֹד בָּֽד׃ [2] 1 Samuel 1:11.