If you're into giving out of obligation, giving because the Law says that you are to tithe 10 %, and if you do, then you have fulfilled your obligation to God, then you understand duty and obligation but not grace. To be honest I easily get 50--50. For example in a friendship, if Mary and I have someone over for a meal, it's easy to expect that they will repay in kind and have us over. This keeps things fair and just, but if we determine our giving and our relationships on fifty-fifty we're going to end up angry because there will be times when it's not even at all. In his letter to the Corinthians Paul stressed a far superior way to determine how we give. It needs to be rooted in Calvary love (1 Corinthians 13) and this is a sacrificial love that leads to generous giving when there is not hope of reciprocation. This joyful, generous giving is not about fairness and balancing the relationship balance sheet. It's about joyfully using gifts to express the infinite love of Jesus and his free gift. Escape from dutiful justice giving. Give out of grace.