"When God expresses his eternal purposes in words, through his prophets, those prophecies will surely come to pass...God sometimes even represents his word as his active agent that inevitably accomplishes his bidding:
Isaiah 55:11 (NKJV)
(As the fruitful rain,)So shall My word be that goes forth from My mouth;
It shall not return to Me void,
But it shall accomplish what I please,
And it shall prosper in the thing for which I sent it."