Albert Barnes Commentary 1 Samuel 2:35

"And I will raise me up a faithful priest, that shall do according to that which is in my heart and in my mind: and I will build him a sure house; and he shall walk before mine anointed for ever." — 1 Samuel 2:35 (ASV)

Zadok is meant rather than Samuel. The High Priesthood continued in the direct descendants of Zadok as long as the monarchy lasted (see 1 Chronicles 6:8–15).

Mine anointed - In its first sense, this term obviously refers to the kings of Israel and Judah (Psalms 89:20; Zechariah 4:14). But doubtless, the use of the term MESSIAH (Χριστὸς Christos) here and in 1 Samuel 2:10 is significant and points to the Lord’s Christ, in whom the royal and priestly offices are united (Zechariah 6:11–15; see the marginal references). In this connection, the substitution of the priesthood after the order of Melchizedek for the Levitical priesthood may be foreshadowed in 1 Samuel 2:35 (see Hebrews 7).