What is Old and What is New

In the Gospel According to Matthew, right after a section of recorded parables, we read this: 

[51] “Have you understood all these things?” They said to him, “Yes.” [52] And he said to them, “Therefore every scribe who has been trained for the kingdom of heaven is like a master of a house, who brings out of his treasure what is new and what is old.” 

Matthew 13:51–52 (ESV)

I have no idea what this means. 

I love it. It is wonderful and marvelous and mysterious. Important truths have been opened to me in the reading of this short little parable. But I don't really know what he is talking about. 

I do know that I genuinely want to be a scribe who has been trained for the Kingdom of Heaven.