17:5 Luke referred to the Twelve as apostles here probably to highlight the importance of this teaching for disciple leaders. Evidently the apostles concluded that such a magnanimous approach to forgiving would require more faith in God than they possessed. They would have to believe that God could change a person's heart who gave no evidence of genuine contrition by repeatedly sinning and then repeatedly professing repentance.
17:6 Jesus encouraged the disciples by reminding them that only a little trust in God's ability can result in unbelievable change (cf. Matt. 17:20; 21:21; Mark 11:23). A mustard seed was proverbially small (cf. 7:13). Mulberry trees grew to be as tall as 35 feet and were difficult to uproot.386This response by Jesus amounted to telling the disciples that they did not need more faith. They just needed to use the faith they had.
"This word of Jesus does not invite Christians to become conjurers and magicians, but heroes like those whose exploits are celebrated in the eleventh chapter of Hebrews."387
17:7-9 Jesus told this parable to teach His disciples that warning sinning disciples and forgiving those who sinned and repented was only their duty. It was not something for which they should expect a reward from God. The Pharisees believed that their righteous deeds put God in their debt, as did many of the Jews. God will indeed reward faithful service (12:35-37, 42-48). However that is not because His servants have placed Him in their debt but because He graciously gives them more than what is just. The teaching in chapter 12 (vv. 35-37, 42-48) deals with the Master's grace whereas the teaching here in chapter 17 (vv. 7-10) stresses the servant's attitude.
Perhaps Jesus selected the example of a servant laboring in the field or tending sheep because this is the type of service His disciples render. In the situation Jesus pictured the one servant had several different responsibilities to his master. Jesus did not picture a large estate in which each slave had only one specialized task. Again the parallel with disciples' duties is realistic. The point is not the master's attitude in failing to express thanks for services rendered but the servant's attitude in doing his duty without placing his master under obligation to him.
17:10 Jesus drew the application. His disciples should have the same attitude as good servants. By claiming to be unworthy they were not saying that they were totally worthless people. They meant that they were unworthy of any reward because all the service they had rendered was simply their duty to their Master. In the context the particular duty in view was forgiving generously (vv. 3-4), but the teaching applies generally to all the duties that disciples owe God.
Jesus and the apostles taught elsewhere that the prospect of reward should motivate disciples to serve the Lord (Matt. 6:19-21; 1 Cor. 3:10-15; 9:24-27; 2 Cor. 5:9-10; 1 John 2:28; 1 Pet. 4:13; 5:1-4). Jesus was not contradicting that here. Here his point was that God is under no obligation to reward us. He will do so because He chooses to do so, not because He has to do so. Our attitude should be that God does not need us to serve Him and that serving Him is only our duty for which He is under no obligation to reward us.
