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Then shalt thou call, and the Lord shall answer; thou shalt cry, and he shall say, Here I am. If thou take away from the midst of thee the yoke, the putting forth of the finger, and speaking vanity; (Isaiah 58:9)

And he came unto his father, and said, My father: and he said, Here am I; who art thou, my son? (Genesis 27:18)

That the Lord called Samuel: and he answered, Here am I. 5 And he ran unto Eli, and said, Here am I; for thou calledst me. And he said, I called not; lie down again. And he went and lay down. 6 And the Lord called yet again, Samuel. And Samuel arose and went to Eli, and said, Here am I; for thou didst call me. And he answered, I called not, my son; lie down again. 7 Now Samuel did not yet know the Lord, neither was the word of the Lord yet revealed unto him. 8 And the Lord called Samuel again the third time. And he arose and went to Eli, and said, Here am I; for thou didst call me. And Eli perceived that the Lord had called the child. (1 Samuel 3:4-8)

Who answers when you call? A person that  knows you answers when you call. Blind Isaac did not know which son was speaking to him. God is not blind, he knows. Young Samuel did not know which spiritual leader was speaking to him, he thought it was Jehovah's representative not Jehovah himself. God is not naive, he knows. If we trust Jesus enough to follow his instructions we can know that he knows us and so he will hear us.