The logic of this belief is deceptively simple. It is taught that giving money to a religious cause is like planting a seed towards God. Those who contribute will receive blessings from the Eternal in direct proportion to the amount of money they give (or 'sow'). Those who give only a small amount of support can expect to receive only a small blessing. Those who contribute or pledge to give as much as they can (even beyond what they can afford), however, can expect an abundant blessing from the Lord. This blessing is for their 'stepping out in faith.'
The appeal of the seed faith teaching, according to the book "Field Guide to the Wild World of Religion," is "with those who feel disenfranchised from the system of prosperity which many in the Western world enjoy" (pages 190 - 191).
One major false assumption revolves around the idea that the Bible promises prosperity and health in this life if only the right "key" or "formula" is utilized. Although Scripture promises prosperity (Revelation 21:7) and healing (verse 4) in the resurrection, no such guarantee exists for this life. In fact, there are times when it is God's WILL that a believer suffer for his sake (1Peter 3:14, 17, 4:16, 19). The apostle Paul, the most influential Christian preacher next to Jesus, suffered trials and troubles all his life. He spent at least five total years of his ministry in prison, was whipped five times, beaten three times with rods, had infirmities (2Corinthians 12:7, Galatians 4:13) and a host of other difficulties. He also experienced being STONED and enduring THREE shipwrecks (2Corinthians 11:23 - 28)!
Another big problem with the teachings of 'seed faith' is the notion that if a believer says or does certain things (e.g. claim a Biblical promise or give money), that God MUST respond in a certain way (e.g. give a blessing). God is all-powerful and can do anything He wishes at any time. Only he knows what is best for a Christian at any given time, which sometimes means he denies their request. Demanding God perform according to a human's understanding of Scripture is tantamount to tempting him. This is precisely what Satan did when he told Jesus to "test" the Biblical formula that God would save him if he fell (see Matthew 4:5 - 7, Psalm 91:11 - 12).