The Lord has revealed to us a little about His infancy and many things about the last three years of His life, culminating in His Passion, death, resurrection, and ascension into heaven. But the Lord has chosen to reveal only one event of the almost thirty years between His infancy and public ministry. The finding of the twelve-year-old Jesus in the Temple is a unique event.
The key to understanding this event may be the fact that Mary and Joseph found Jesus on the third day (Lk 2:46). This is an intimation of Jesus' resurrection from the dead on the third day. In a very subtle way, Luke may be saying that Jesus' childhood and adulthood consisted of many prefigurements of His Paschal mystery.
This also is the meaning of our lives in Christ. We have been baptized into Jesus' death and resurrection (see Rm 6:3ff). We are continually carrying about in our bodies the death of Jesus (2 Cor 4:10), while we have already been raised up in company with Christ (Col 3:1). Our lives should be patterned on sharing in Jesus' sufferings (Phil 3:10), and we already live the risen, eternal life when we live our baptismal promises (see 1 Jn 5:13).
Recently, I was speaking to some seminarians. They joked that whenever they didn't know an answer on a theology test, they wrote "Paschal mystery." This is true of life in Christ. It is all about living the Paschal mystery every day in thousands of ways.