You’ll notice I’ve linked to a the King James translation for these scriptures (instead of the usual default). To my ear, it does the poetry more justice than a modern translation does.
It all revolves around the greatness of God:
For I proclaim the name of the Lord:
Ascribe greatness to our God.
He is the Rock, His work is perfect;
For all His ways are justice,
A God of truth and without injustice;
Righteous and upright is He.
… and the Israelites’ sinfulness: their inability to live up to His standards in their own strength. Moses saw how they would fall away from God and what the consequences would be.
And let’s face it: who could do better? There is nothing that we can hide from God.
You have set our iniquities before You,
Our secret sins in the light of Your countenance.