Theodoret of Cyrus
Why did Samuel construct an altar, given that God's law prescribed worship in a single location? The holy temple had not yet been established, and God was worshipped in various places. This reveals that God intended to confine divine worship to one location, being fully aware of humanity's tendencies toward unrighteousness. For the faithful and those who comprehended the intent of the law, any space could be consecrated for the worship of God. Indeed, the esteemed Elijah, despite the law directing all to the sacred temple, built an altar and conducted a sacrifice on Mount Carmel.