Reciprocity for a Soul
Throughout history, there's an idea that is almost universal. It's most commonly referred to as karma today. It is often thought of as some sort of cosmic level of quid pro quo—that if you do good, the "universe" is somehow obligated to reciprocate your good—and likewise your evil. This erroneous philosophy has been long since disproved, most obviously by the book of Job in the Old Testament, and very succinctly by 1 Peter 2:20 in the New. One might argue that Christianity is, in the final analysis, karmic in nature since God in the Judgment will render unto all according to the life they lived here on this earth. True, we will be rewarded according to our works in life (Matt. 16:27), whether good or bad, but the works themselves do not merit anything. The opportunity for salvation has been granted us by grace, but it also requires our obedience (from which come the works God commands of us to be saved). Man's meager attempts cannot prove his own inevitably-deficient righteousness.
The point is: karma isn't true in this world. The idea of repaying good for good, though, is something that is expected of God's people. It has always been so—under the Law of Moses and now under the Law of Christ. "Do not withhold good from those to whom it is due, when it is in the power of your hand to do so" (Pro. 3:27). In the context, that verse involves debts and lending between neighbors, but the principle is easily and logically extendable to every social interaction. If someone does another person good, even in some small way, he should do so for him in return and without undue delay. Doing so serves as a very good Christian example for those around us and builds up friendships.
Paul poses the sentiment in that proverb from Solomon as a question: "If we have sown spiritual things for you, is it a great thing if we reap your material things?" (1 Cor. 9:11). This, coming from the most prolific missionary of the 1st century (and perhaps of all time), places great emphasis on how we ought to treat our brothers and sisters especially. More than any other blessing, we ought to be grateful to God and our teachers for the spiritual blessings we have. It is significant also that Paul goes on to say that he and Barnabas didn't oblige the Corinthian church to help them materially (1 Cor. 9:12-15). Instead, they exhorted them in the same way all are exhorted by the Gospel—through invitation, not force.
RECIPROCITY… (CONCLUSION)
The expectation for us is to carry out half of what people think of today as karma, but the other half we shall not; true, we repay good for good, but we also repay "no one evil for evil" (Rom. 12:17a). Vengeance belongs to the Lord (12:19), and justice in this world to civil authorities (13:1-6). We reciprocate good so that Christ will be glorified. We also return good for evil so that we ourselves are not overcome with evil (12:21).
It is wrong for anyone to expect that every need/want be handed to them simply because they think they've been "good enough," as if God is Santa Claus. This would require God to intervene in every instance of injustice (which He could do but chooses not to). We too should not desire that. If He operated in such a way, our life here would not be a test; we might as well be toddlers micromanaged by an overbearing parent.
None of this is to say He doesn't provide us with blessings in this life, or that He doesn't act by providence; He surely does. But a great deal of the onus is on us to perpetuate good in this life because we become Christ-like the more we do. The upshot of acting appropriately is that we are able to bring souls to Him.