The Bible clearly teaches that God uses human agents to spread Jesus’ message of forgiveness (Mt. 28:18-20; Acts 1:8; 1 Cor. 3:9; 2 Cor. 5:20; Rom. 10:14). And yet, God did not need to use humans to spread his message. God could’ve used angels to spread his message (Rev. 14:6), and yet, he chose to use humans instead. The question is why? The Bible doesn’t directly answer this, but we can speculate a few answers.
First, God may have chosen to work within the parameters of certain rules or laws, which arise from his own nature and plan. For example, consider the book of Job. When we read the book of Job, we see that this epic battle is ultimately a war between God and Satan (Job 1-2). Satan made an accusation that Job was only following God for his blessings.
Readers of Job often wonder, “Why didn’t God just destroy Satan with a cosmic bolt of lightning, forever silencing his accusations?” But, instead of annihilating Satan, we read that God allowed Satan to live. The question is why? Forster and Marston explain,
We may indeed accept that he had the sheer power to stop or even destroy Satan. The problem is that in this case, even as Satan sank under God’s wrath and destruction, he would have gone with a sneer on his lips as though to say, ‘I told you so.’ Such a ‘solution’ would have left forever unanswered Satan’s accusation that God’s kingdom was based (like his own) on force and expediency. It was not lack of power that prevented God from crushing Satan –it was a matter of principle. It is, perhaps, comparable to the moral restraint that makes it impossible for God to lie. Satan’s accusations must be answered, and they cannot be truly answered by a force that simply crushes the accuser.
Once Satan made his accusation against God’s character, it couldn’t be unmade. God had to defeat this accusation –not through violence –but through a demonstration of love (Rom. 3:26; Col. 2:14-15). Instead of killing Satan, God allowed Satan to kill his Son. Instead of looking like a cruel and self-serving tyrant (thus fulfilling Satan’s accusation), he took the form of a slave, and he hung naked on a Roman cross (Phil. 2:5-9). Choosing these rules of engagement, God put down the accusation that he is self-serving in the most unthinkable way possible: the Cross of Christ. Was God required to choose this method? Of course not. God isn’t required to do anything. Instead, he chose to defeat Satan’s accusation in this way.
As we consider God’s wisdom in purchasing our salvation on the Cross, we need to consider his wisdom in spreading this salvation from the Cross. If God spread the gospel through force, it might only revive Satan’s accusations. God may have put himself under these rules of engagement to allow men to choose him out of love, rather than out of fear. For instance, even Reformed thinkers admit that God will sovereignly choose to place himself under certain rules. For instance, Fernando writes,
When the Bible says that all things are possible with God it means that all things are possible with God within the rules that God in his wisdom and sovereignty has set as necessary for a good creation… The boundless saving power of God is limited by the way God ordained to save people –the way of faith.
If there are certain rules in regards to receiving salvation, perhaps there are certain rules in regards to spreading salvation. What are these rules? We might not have a clue. But, perhaps, God is defeating cosmic accusations through the spreading of the gospel by using human agents.
Second, God might receive a greater glory using broken and fallen people. Consider the old show MacGyver. In almost every episode, MacGyver would break out of prison with nothing more than a toothpick, some dental floss, a match, and some rubbing alcohol. He would use the worst materials to bring about the best results. Some people would rather have just seen MacGyver use a key and a gun to break out of prison, but by using scraps, MacGyver showed his brilliance and ingenuity in a way that wouldn’t have been otherwise possible. In the same way, when all the dust settles, God will have used the worst possible people to bring about the greatest possible result (1 Cor. 1:26-29).
Third, God speaks powerfully through fallen people. Many people are often cynical of decrees given by the boss of their company, but they are willing to listen to a coworker more readily. Perhaps, by listening to a fellow sinner, God’s message is easier to accept. Moreover, our usefulness does not pertain to this life only. God will use restored human agents for the ages to come (Eph. 2:7).
Fourth, God might enjoy giving his children responsibility. In a parent-child relationship, the parent enjoys allowing the child to learn to do things on their own. It could be that God wants people to learn to do spiritual work like him. By using human agents, God teaches people about love and patience (Mt. 5:46) –an invaluable commodity.
Fifth, while it is a mystery why God uses people, it is also a privilege. The fact that God uses people means that God wants to give us an incredible purpose in life, impacting eternity.
Sixth, Jesus designed his message of forgiveness, so that it would be as simple and easy to communicate as humanly possible. Wouldn’t it be cruel if Jesus made his message so complex that only a PhD could understand it? He didn’t. He made it easy to understand, so it would spread with ease (Mt. 11:25; 2 Tim. 3:14-15).
Seventh, if we should hope for a single message to be true, we should hope that it is Jesus’ message. If there is only one message that can bring us to God, then let’s hope that it is Jesus’ message, because it has reached the most people in the least amount of time.
Ultimately, it is a mystery as to why God uses human agency. But, according to the Bible, it is not a mystery that he uses human agency. While we can speculate about this subject, if we trust the biblical account at all, we see that humans have a vital role in reaching the world for Christ.
 Forster, Roger T., and V. Paul Marston. God’s Strategy in Human History. Minneapolis, Minnesota: Bethany House Publishers, 1974. 8.
 Emphasis mine. Fernando, Ajith. Crucial Questions about Hell. Eastbourne, E Sussex: Kingsway Publications, 1991. 91; 92.
 This does not mean that these rules are “above” God, but he might willingly put himself under these rules. This concept should not surprise any Bible reader, especially when we consider subjects like Christ’s incarnation. God is willing to humbly put himself under rules, which would seem incredible to us.