Yea, before the day was - Before the first day, or before the beginning of time; from eternity. The Septuagint renders it correctly, Ἀπ ̓ ἀρχης Ap' archēs, and the Vulgate (Ab initio), ‘From the beginning.’
I am he - I am the same Isaiah 43:10.
I will work - I will accomplish my designs.
And who shall let it? - Margin, as Hebrew, ‘Turn it back.’ The meaning is, ‘Who can hinder it?’ And the doctrine taught here is:
1. That God is from everlasting, for if he was before time, he must have been eternal.
2. That he is unchangeably the same - a doctrine which is, as it is here designed to be used, the only sure foundation for the security of his people - for who can trust a being who is fickle, changing, vacillating?
3. That he can deliver his people always, no matter what are their circumstances.
4. That he will accomplish all his plans; no matter whether to save his people, or to destroy his foes.
5. That no one - man or devil - can hinder him. How can the feeble arm of a creature resist God?
6. That opposition to him is as fruitless as it is wicked. If people wish for happiness, they must fall in with his plans, and aid in the furtherance of his designs.