God's Support and Protection
God sends His messengers to deliver His message - and He ensures they succeed. The obstacles placed before them by those who reject the message are never left to chance or to the messenger's own resources alone. God intervenes, schemes against those who scheme, and guards His messengers against those who would silence them before their mission is complete:
[5:67] O you messenger, deliver what is revealed to you from your Lord - until you do, you have not delivered His message - and GOD will protect you from the people. GOD does not guide the disbelieving people.
[9:40] If you fail to support him, GOD has already supported him. Thus, when the disbelievers chased him, and he was one of only two in the cave, he said to his friend, "Do not worry; GOD is with us." GOD then sent down contentment and security upon him, and supported him with invisible soldiers. He made the word of the disbelievers lowly. GOD's word reigns supreme. GOD is Almighty, Most Wise.
[8:30] The disbelievers plot and scheme to neutralize you, or kill you, or banish you. However, they plot and scheme, but so does GOD. GOD is the best schemer.
The Scope of Protection
This protection is specific in its scope. It is protection against those who seek to prevent the message from reaching its destination - against persecution, exile, and assassination. It is not a shield against human fallibility. The messengers of God are, in every other respect, accountable human beings who are capable of error and subject to divine correction, just as the rest of mankind is. The Quran documents the mistakes of numerous prophets and records God's direct reprimands of Muhammad on multiple occasions. A man whom God protected from his enemies, God also corrected when he erred. These two facts are not in tension - they are complementary. One tells us that God's message will always reach its people. The other ensures that no messenger is elevated beyond his station into something he was never meant to be.