The Childhood of Jesus christ

The Childhood of Jesus christ described in the Gospel in Luke 2: (40-52) of the story one.This part is divided into three.
(1) First, Section 40. "Young children grow and grow stronger, full of wisdom, and the grace of God is upon them."
(2) Next, it will be described in more detail what happened in the temple when he was 12 years old. The Childhood of Jesus christ (Verses 41-51).
(3) The last part is over. "Jesus is much more" Wisdom added, height increased, and loved by God and people "(verse 52)

This verse 52 is the same sentence as the previous verse 40, although the words are different. It's weird, I wonder why it is written the same thing over and over again? Luke is the only one who tells of the 12-year-old boy Jesus, and it does not appear in other gospels. The problem with this story itself is whether it is really there or is it just a story to teach？Let's think about what is the story of this part of the sentence, the idea of the author who wrote it, and the purpose of what he wrote for. I wondered what he put in such a story on purpose to say what.

(1) This story appears only in Luke Gospel. But there was no beginning in Luke Gospel. It does not appear at all in other gospels or Paul's letters, which he adds later. John's authors, etc., surely read and read the Gospel of Luke, but still say nothing about the birth of the Lord Jesus or his childhood.
(2)This story concludes a series of stories about the Lord's birth in the Gospel of Luke. Moreover, this part is integrated into one, independently of the sentences before and after it. It doesn't even follow. Originally, this was an independent story. The author incorporated it into his gospel.