Passage
and they did not understand the saying that he spake to them,
and they did not understand the saying that he spake to them,
Luke 2:48 And, having seen him, they were amazed, and his mother said unto him, `Child, why didst thou thus to us? lo, thy father and I, sorrowing, were seeking thee.'
Luke 2:49 And he said unto them, `Why <FI>is it<Fi> that ye were seeking me? did ye not know that in the things of my Father it behoveth me to be?'
Luke 2:50 and they did not understand the saying that he spake to them,
Luke 2:51 and he went down with them, and came to Nazareth, and he was subject to them, and his mother was keeping all these sayings in her heart,
Luke 2:52 and Jesus was advancing in wisdom, and in stature, and in favour with God and men.
The verse centers on "understand", "saying", and "spake". It is saying that the verse draws attention to "understand" and "saying", so its meaning should be read from those terms before moving to application.
The nearby context moves from verse 49's "And he said unto them Why FI..." into verse 51's "and he went down with them and...", so "understand" and "saying" belong inside that flow. In Luke context, the local focus is Christ, faith, and discipleship.
A plain takeaway is to answer the verse's own emphasis on "understand" and "saying" with trust shaped by these words, not by a vague optimism outside the passage.