Verses 25 and 26 essentially repeat verses 23 and 24.
Verse 23 said they should continue to observe the Sabbath. Verse 25 has them set aside a day when they should worship. Particularly in an agrarian society, there was much labor in the growing season, and it would be unusual to take two different days off for worship. Thus, verses 23 and 25 are different ways of saying the same thing.
Similarly verses 24 and 26 both indicate that the priests are to work for their own support. Why repeat these things? The repetition serves to emphasize their importance. As a new community, there are two principles that will become part of the bedrock actions of the community: They will observe the sabbath to worship God, and their priests will not depend upon the people for their support, but they will work with their own hands.