This verse is part of a section in 1 Chronicles chapter 25 that describes how King David organized the musicians who would serve in the temple. Let's break it down:

"Now the first lot came out for Asaph to Joseph...": This means that the first group selected by lot (a form of drawing lots to make a decision) was assigned to Joseph, who belonged to the family of Asaph. Asaph was one of the key leaders of temple musicians appointed by David (see 1 Chronicles 6:39, 15:17, 16:5). The phrase "came out for" suggests that the first turn to serve in the temple musical service was given to this division.

"the second to Gedaliah, he and his brothers and sons were twelve;": The second group selected by lot was assigned to Gedaliah. This group consisted of Gedaliah himself, along with his brothers and sons, totaling twelve people. This indicates the size of the musical group.

In essence, the verse describes the allocation of musical duties within the temple, assigning the first turn to the group led by Joseph from the Asaph family, and the second turn to Gedaliah's group, which comprised twelve members.

Contextual Understanding:

To fully grasp the meaning, it's crucial to understand the broader context:

Organization: David meticulously organized the temple services, including the musicians, to ensure smooth and efficient worship.

Division of Labor: The musicians were divided into groups, each led by a specific leader. This allowed for a rotating schedule and balanced workload.

Drawing Lots: The use of lots was seen as a way to seek divine guidance in assigning duties and responsibilities. It was considered a way to leave the decision to God.

Family Groups: The musicians often worked in family groups, passing down their skills and traditions from one generation to the next.

The verse highlights the systematic and divinely-guided approach to organizing the temple's musical services, emphasizing the role of specific individuals and family groups in carrying out these responsibilities.