Numbers 1 is a census of the tribes of Israel, taken at the beginning of their wilderness journey after leaving Egypt. Verse 6, "Of Simeon: Shelumiel the son of Zurishaddai," simply identifies the leader or representative chosen from the tribe of Simeon to participate in the census.

Let's break it down:

"Of Simeon:" This specifies that the following information pertains to the tribe of Simeon, one of the twelve tribes of Israel.
"Shelumiel": This is the name of the man chosen to represent the tribe of Simeon.
"the son of Zurishaddai": This identifies Shelumiel's father as Zurishaddai. This was common practice in biblical genealogies, serving to connect individuals to their lineage and establish their family identity.

In summary, the verse means:

Shelumiel, whose father was Zurishaddai, was selected to represent the tribe of Simeon in the census described in Numbers chapter 1.

Significance:

This verse is part of a larger enumeration that demonstrates God's faithfulness in multiplying the descendants of Jacob (Israel).
It highlights the tribal structure of Israel and the organization imposed upon them as they prepared to inherit the Promised Land.
The leaders chosen, like Shelumiel, were likely men of importance and influence within their respective tribes.

It's a small piece of a larger story about the organization and preparation of the Israelites as they moved from slavery to nationhood.