וַיֵּ֧לֶךְ אֶלְקָנָ֛ה הָרָמָ֖תָה עַל־בֵּית֑וֹ וְהַנַּ֗עַר הָיָ֤ה מְשָׁרֵת֙ אֶת־יְהוָ֔ה אֶת־פְּנֵ֖י עֵלִ֥י הַכֹּהֵֽן׃
Und Elkanah ging nach Rama zu seinem Haus. Und das Kind diente dem HERRN vor Eli, dem Priester.
Rashi on I Samuel
Served Adonoy in the presence of Eili the kohein. From here [our Sages conclude] that "whoever serves before a Torah scholar is considered as though he had served before the Divine Presence."8Talmud Yerushalmi Eruvin 5:1. The reason being that a Torah scholar cleaves to ‘ה in his thoughts at all times so that even his physical activities are holy.
Metzudat David on I Samuel
In the presence of: Meaning to say, in front of him. For he was teaching him how to serve the Lord.
Radak on I Samuel
Upon (al) his house: It is like, to (el) his house. Likewise (I Samuel 1:10), "So she prayed upon (al) the Lord," is like, to the Lord.