The law of sowing and reaping

Karma. What goes around come around. You will reap what you sow. Various believers and non-believers, religious, not-so-religious, and irreligious, may express a view of the law of cause and effect in such terminologies. Everything happens for a reason. All actions (and even inactions) have consequences. The consequences occur in specific results (effect) created by the action (cause). Contra Meg Ryan in Proof of Life -- who said, "Things don't happen for a reason, they just happen" -- most people have some attachment to this idea.

Many consider this a law of nature -- whatever action we take, there is always a reaction. No doubt so many believe in cause and effect because it is supported by their experience. Non-believers may attach the idea to fate. In Hinduism and Buddhism it is karma* -- a person's actions in this life decide his or her fate in future life. Islam's writings agree: And said, "If you do good, you do good for yourselves; and if you do evil, you do it to yourselves" (Qur'an 17:7, Sahih International). In The Doctrine and Covenants 130:18-21, Mormonism's founder Joseph Smith teaches that God's blessings (effect) arises from obedience (cause), and that these continue into the next life. In the Bible we read, "Whatsoever a man soweth, that shall he also reap." I'm no expert on all the world's religions, but it appears that most religions espouse a law of cause and effect.

There is a "Law of Cause and Effect"
The Bible teaching of this principle can be found in various teachings and sayings.
Obadiah 15 For the day of the LORD is near upon all the heathen: as thou hast done, it shall be done unto thee: thy reward shall return upon thine own head.
Matthew 26:52 Then said Jesus unto him, Put up again thy sword into his place: for all they that take the sword shall perish with the sword.
Galatians 6:6-8 Be not deceived; God is not mocked: for whatsoever a man soweth, that shall he also reap. For he that soweth to his flesh shall of the flesh reap corruption; but he that soweth to the Spirit shall of the Spirit reap life everlasting.
Cf. also Job 4:8; Proverbs 11:18; Proverbs 11:24; Proverbs 22:8. This principle deals with all of life, natural and spiritual.If you plant a field of corn you will reap a crop of corn. If you sow to the wind, you will reap the whirlwind. One becomes a victim of the consequences of his own actions.

A few Bible examples
Positive
The widow of Zarephath used the last of her flour and oil to make a cake for Elijah and received in return a continous supply of meal for the duration of the famine. See I Kings 17:10-16
The disciples dispensed fragments of the loaves and fishes, and received back a basketful each. See Mark 6:41-43

Negative
Haman hanged on the gallows that he built for Mordecai. See Esther 7:9-10.
Edom joined Babylon in rasing Jerusalem, and were themselves in turn by destroyed as a nation. See Obadiah 8-15.

General truths of sowing and reaping.
1. A law of reproduction. You reap in kind what you sow. Corn yields corn; apples yield apples, etc. (Genesis 1:11; Galatians 6:8).
2. A law of order or process. Sowing precedes reaping (1 Corinthians 3:6; implies a wait).
3. A law of increase. You reap more than you sow (Matthew 13:8). 
4. A law of proportion. The more you sow, the more you are likely to reap (2 Corinthians 9:6). This is directly related to point three, but subtly different.
5. A spiritual law. For example, if you sow in sin, you will reap God’s judgment.

The Law of Cause and Effect serves God
The law of cause and effect serves and is subject to God. God does not serve it. It is not a law that operates independently of God. God is not only bends the laws of nature to His own purposes -- the sun standing still, storms being stilled, etc. -- He also supersedes His laws in the spiritual realm. Thus it is that, though we are sinners, we can be forgiven of God and escape the consequences of our sins. By law, yea, even the law of cause and effect, we should suffer eternal punishment for our sins. By God's abrogation of the law of cause and effect, Jesus is punished for our sins and we are set free from the law of sin and death.

Friend, the law of cause and effect is real. You will reap what you sow. God's grace and mercy is awesome. Cast yourself upon it.

“Shallow men believe in luck or in circumstance. Strong men believe in cause and effect.” -- Ralph Waldo Emerson

* "In short, Karma is the law of cause and effect in the ethical realm." Nevertheless karma as an ethical teaching is based on the Eastern idea of reincarnation. It has similarities to the law of sowing and reaping, but is not based on the Bible.
Cf. also "He who wishes for the tilth of the next world, we will increase for him the tilth; and he who desires the tilth of this world, we will give him thereof, but in the next world he shall have no portion." Surah 42:19