When Samuel is a child, God calls him three times. This is a time when “the Word of the Lord [is] seldom heard, and no vision [is] granted.” (1 Samuel 3: 1) Samuel is in the service of Eli; sleeping in the temple of the Lord where the Ark of the Covenant is kept. Samuel does not know the Lord; the Word of the Lord has not been disclosed to him. Yet, God calls him three times.
God calls a child who does not know Him; He calls him into His service. God appoints Samuel His prophet even before the child knows Him.
When God calls, Eli instructs the child in his service to respond, “Speak; Your servant hears You.” (1 Samuel 3: 11)
Samuel obeys Eli. As he grows up, the Lord is with him. And all of Israel recognizes that Samuel is confirmed as a prophet of the Lord. “So the Lord continues to appear in Shiloh, because He revealed Himself there to Samuel.” (1 Samuel 3: 21)
The Lord calls; the Lord reveals Himself before we know Him; before His Word is disclosed to us.