Exodus 34:6 - Matthew Poole's English Annotations on the Holy Bible

The Lord God: this title shows his glorious being, power, and authority; the following titles note his goodness to men. Abundant in goodness and truth; in fulfilling all his gracious promises made to Abraham, and to his seed, and to all his people; wherein he is said to be abundant, because he generally is better than his word, and gives more than he promised. There is a truth in Divine threatenings, but here the situation of this word in the midst of the attributes of Divine goodness plainly shows that it is to be restrained to the promises; this being usual and reasonable, that general words have their signification limited by the context. And indeed here seems to be a hendyadis, goodness and truth, for true, sincere, and hearty goodness, as mercy and truth are oft put for true and real mercy. See Psalms 25:10, Psalms 57:3, &c.