6b “The LORD, the LORD God, merciful and gracious, longsuffering, and abounding in goodness and truth"
my first thought was to answer, "the LORD" but feared I'd be read in a characteristic that is common to me
But that "the LORD" is repeated here does seem to indicate a necessity, by merit of being God's Word, rather than a redundancy. It implores us that we should pay double attention, imo. And indeed, we can compare characterizations of the LORD against this verse to determine whether He is known amongst them who proclaim it, as this is within the context of God proclaiming His Name.