# rejoice before Yahweh

"rejoice in the presence of Yahweh"

# the Levites who are within your gate

"the Levites who live inside your city" or "the Levites living with you" 

# because he has no portion or inheritance among you

The fact that Yahweh would not give any of the land to the Levites is spoken of as if a father were not giving them an inheritance. 

# he has no portion

"they have no portion". Here "he" refers to Levi. Levi represents all of his descendants.