# As Yahweh lives

"I solemnly swear"

# the nations will bless themselves in him

"people of other nations will bless themselves in me". The word "him" refers to Yahweh. 

# the nations will bless themselves in him

"the people of the nations will ask Yahweh to bless them"

# in him they will glory

"they will boast in me" or "they will praise me".