Having exposed the flawed law-obedience of the Pharisees, Jesus warns his disciples of the danger of adopting the same heresy and in so doing, cause young believers "to fall away" from God's grace. The episode consists of a saying on stumbling-blocks, followed by a saying on forgiveness that reinforces the foolishness of trying to win brownie points from God, given that no person, other than Jesus, has ever been able to forgive "countless times." In a third saying, Jesus reveals the one law demanded of his followers, namely faith, and points out how even the most feeble faith activates God's unlimited love. This is followed by a teaching parable which serves to summarize the issue at hand, namely, the flawed law-obedience of the Pharisees. Even if a person were to have done everything demanded of God's law, they would still have no claim on him. We stand approved before God as a gift of grace, appropriated through faith, and not works of the law.
 v1-2. Addressing his disciples (in particular those who, because of their position in the church or their Christian maturity, have some influence over younger believers), Jesus warns them not to cause a believer (a "little one") to turn away from him. It's very easy for mature Christians to mimic the Pharisees' belief that a person's standing with God is somehow maintained, even improved, by a rigorous attention to God's law. Let us take care that we never lead a young believer away from God's grace.
v3-4. God's law can be encapsulated in the command to love our neighbor, and the most practical expression of mutual love is found in forgiveness. Yet, is there anyone who could claim to have forgiven a brother "countless times"? The disciples certainly recognized the problem. A brother/sister may need rebuking, but above all they will need forgiving, accepting, including, .... and that's the hard call. Jesus' words serve to remind the disciples of their inability to be worthy of God through their own effort, and thus of the stupidity, even danger, of teaching the way of law-righteousness to "little ones."
v5-6. The truth is that there is but one law and that law, that eternal demand of God, is the exercise of faith in Jesus Christ for salvation. The disciples have asked for a faith to do, but Jesus offers them a faith to receive. Jesus reminds them that even the most hesitant and questioning reliance on him can activate God's eternal acceptance, and this against all odds. Rather than laying on the "little ones" the "yoke" of the law, lay on them the yoke of faith.
v7-10. Jesus has made the point to his disciples that they must take care that they don't adopt the law-obedience of the Pharisees, given its power to undermine the way of salvation. In the end, our standing before God is a gift of his kindness. We can earn nothing from God, for we always remain "unworthy servants." Jesus now illustrates this truth in a parable. Were we to have completed everything that was commanded of us, we would still have to admit that we can claim no extra benefit from God, no increased status or reward, for in the end, complete obedience is but our duty.
 It has long been recognized that a child's perception of God is influenced by their parents. If a child's parents are dictatorial, harsh, judgmental, even violent, then the child often perceives their heavenly Father in similar terms. The Bible's high standards for parenting reflects the important heavenly image provided to children by their parents. Positive parenting reveals the character of God to children.
In a similar way, the mature members of a Christian fellowship serve as role models for God's character. The new believer will often image God in terms of the behavior of older believers. If the older members are judgmental, demanding, strict, overly pious, legalistic, ..... then the new believer will tend to see God in these terms.
Jesus therefore makes a point of warning his disciples of the danger of setting before a young believer "things that cause people to sin", "temptations to sin", RSV., or better, "stumbling-blocks" (alternate reading). Although such "temptations" are often seen in terms of say, offering someone a drink of alcohol, Jesus has in mind a far greater "sin". He does not want the "older brother" to undermine the faith of the "weaker brother, such that the weaker brother looses touch with Jesus.
The most dangerous example set by a mature believer is that of nomism, the idea that law-obedience both restrains sin, thus maintaining a person's standing before God, and promotes holiness, thus progressing their standing before God for the full appropriation of his promised blessings. If we are harsh and demanding in the pursuit of our own self-righteousness, a new believer can easily pick up on our piety and so after beginning with the Spirit end up trying to attain their goal by human effort, Gal.3:3.
We all "fall short of the glory of God" and are in need of correction, but even more so, we all need God's forgiveness. Oh yes, we pretend that we are all loving, but in our heart of hearts we know we fall short. And even if we didn't fall short, which is impossible, we would still be "unworthy servants" - we don't get brownie-points for doing what we're supposed to do. Thankfully, faith in Christ accesses God's total love for us, and so the only load with which we should burden a young believer is the yoke of faith, through which we all access God's grace.
 Having forgiven "we have only done our duty." Why is there no reward?