2. The examples of Abraham and Jacob are not normative patterns. 

Some think tithing is required because both Abraham and Jacob gave a tenth, and they both lived before the Mosaic covenant was in place. Such examples hardly prove tithing is for all time, however. Abraham’s gift to Melchizedek was a one-time event; there is no evidence he regularly gave God a tenth.

Jacob’s giving of a tenth signified his gratefulness to God for promising to be with him and to protect him. His gratefulness and generosity still speak to us today, but a historical description of what Jacob gave doesn’t support the idea that all believers must give God a tenth of their income.