When Jesus was 12 he went with his parents to the annual Passover Celebration.
The Passover is a Jewish Celebration to remember when God brought the Israelites of Egypt. This was the last plague God put on the Egyptians. The Angel of Death was to fly over and kill the first born of ever family. To save the Israelites Moses Told them to put sheep's blood above the front door of their houses. Then the Angel would see it and pass over the Israelite Families. The Angel of Death killed the first born of every Egyptian family. The Israelites had to leave Egypt in a hurry when the Pharaoh finally gave them Permission to go and they didn't have time to let their bread rise. So they baked flat bread.
So Mary, Joseph, Jesus, friends and relative went to Bethlehem for the festival. They all had a good time at the end of the week they headed back to Nazareth. Mary and Joseph thought Jesus was with friends or relatives so they didn't worry too much. At the end of the first day, when they could not find Jesus, they turned around and went back to Bethlehem to find Jesus. They looked for 3 days for Jesus all over Bethlehem.
Now 3 is a very common number in the Bible going all the way back to Adam and Eve. Adam and Eve had 2 sons Cain and Abel. After Cain killed Abel Eve had another son, Enoch, that made 3 sons. Noah had 3 sons Ham, Sham, and Japheth . Moses' family consisted of 3 Marion, Aaron and Moses. There were 3 men thrown in the fire for not bowing to the King, Shadrack, Meshack, and Abednego.
In the New Testament Jesus was tempted 3 times. At the transfiguration there were 3 standing there. There was Jesus, Moses and Elijah. Jesus rose from the dead on the 3rd day. And we worship the Trinity, God the Father, God the Son and God the holy Ghost. There were many more instances where 3 is used in the Bible. These are the ones that come to my mind first.
On the 3rd Day Mary and Joseph decided to search the temple, They had searched the rest of Bethlehem with no luck. When they walked in, there was Jesus talking with the church elders. Jesus was asking and answering questions. The church elders were amazed at his knowledge. When Mary came in she was probably like most mothers. She probably started crying with relief and went over and hugged Jesus. Then she asked him why he stayed in the temple.
Jesus answered Didn't you know I needed to be in my fathers house?
Everyone was surprised with his answer and Mary remembered it the rest of her life. Then they went back to Nazareth. After that Jesus was very obedient to both Mary and Joseph.