Jesus had come to earth for a specific purpose; to save mankind and take the souls to Heaven, that is why He is the only way, the truth and the life. He was fully God and fully human. He was lost in the temple when He had gone for the feast of the tabernacle and was in discussions with the learned priests, who were at a loss to see a little boy of 12 debating with them and that too without any formal learning. His parents searched for Him everywhere, He was no where to be found, no one seemed to know where He had gone and finally after three agonising days, they found Him in the temple. There was joy and anguish and when His mother asked Him as to why did He agonise them, He calmly replied that He was doing His fathers will. This shows that He was God and Man.
This passage mentions Joseph, His foster father, for the third and the last time. The three days of being lost can be inferred as three days after the death and finding would refer to the resurrectionBeautiful food for thought.
The Lord allowed himself to be lost for a moment, so that Joseph and His mother might understand the plan of salvation which was to be accomplished in Him.