These words are found a few times in both the old testament and the new testament.
Abraham, Jacob, Moses, Samuel, Isaiah, David in the Psalms, and Jesus, attributed to him in Hebrews, and in Revelations, all say these words in response to the Father.
They are words that are accompanied by action and are spoken in the presence of God.
The words are not intended simply to reveal the speakers location, like in a game of hide and seek. They are actually an announcement of a willing servant ready to listen and follow orders. Like a soldier volunteering for duty, no matter how dangerous.
When he was about to be tested and then, when he was about to sacrifice Isaac, Abraham heard his name called by the angel of God, and he replied "here I am".
Samuel was asleep before the ark of God, when he arose to his name and went to Eli three times with the same response, the last time Eli explained that it was in fact God calling, and the appropriate response was "Speak Lord for your servant is listening".
When Isaiah heard the proclamation "whom shall I send?", his reply was "Here I am, send me"
And Jesus in Hebrews as well as in the psalm states "Here I am, I have come to do your will".
Wonderful deep words that speak of the humble obedience of those who trust God.
But in reality, it is a big struggle to joyfully obey for even the most devoted Christian.
That adds to the beauty and grace of the words in Hebrews, "Here I am, and the children you have given me".
Those children are people like us. People who believe in Jesus. Who love him because we somehow have realized what a wonerful thing he has done for us by giving himself up to die on a cross.
Somehow, but without doubt, he took us up into that cross, we died with him, crucified, and have been given a full share of his obedience. He can, and does do this. His perfect "Here I am" becomes our perfect "Here I am".
This is a gift.
The gift is servanthood.
All God's children are servants.
Let us serve one another, humbly and joyfully.
We truly have a magnificent Saviour, the Lord Jesus Christ.