This passage seems at first glance to reduce God, through anthropomorphisms, to human fallibility or at least human finitude. It can be disturbing to Christians who need their God to be sovereign. I believe that we can justify these answers by remembering that God's sovereignty encompasses everything that happens in His heaven and earth, including the intercession of His servants. Human prayer is one of those 'events' in history which God has ordained and chosen to use in order to bring about His eternal purpose.
Historical prayer plays a most instrumental role in the eternal plan of redemption.
God knows our prayers even before we voice them. It is His Spirit who gives us the faith to pray, who provides the words in our mouths, and who prays with us with groanings too deep for words. God has taken our prayers in Him into account from eternity. Moses prayed in the Spirit of Christ, and therefore, and for no other reason, his prayers were effectual. It is only as we are accounted in Christ, the righteous Man, through Spirit-worked faith, that we are clothed with His righteousness, and that our prayers avail much before the Father.