In your question you use the words “have to.” These are words that express a forced motivation, an obligation. When a Christian gives any amount to the work of the church, it is done out of a sense of thankfulness and appreciation to God for all that He has done for us. A Christian gives to support the ministry of the church because he wants to, feels privileged to do so, not because he “has to.”
In the Old Testament Scriptures God gave His people different types of laws. One type of law was called “ceremonial”, which governed their worship life. These ceremonial laws were meant to keep Israel as a tight knit nation, until the Savior Jesus Christ came. Some of these ceremonial laws specified the outfits the priests would wear, the sacrifices, foods they would eat, the tithe, festivals and Sabbath days. When Jesus came and completed his ministry, these ceremonial laws were no longer necessary. Many of them were a like a shadow, prefiguring to the work Jesus Christ would accomplish.
As we look at the tithe, we see that it had a threefold purpose : 1) to support the Levites, 2) to support the Feasts, and 3) to support the less fortunate . . . all to remind God’s people of his presence and faithfulness.
In the New Testament Scriptures there is no mention of mandatory tithing as a principle for determining how much to give. The New Testament nowhere encourages the use of the tithe but does criticize those who use it self-righteously (Lk. 18:12). Although a Christian is free to use the tithe as a guide for himself, ten percent for some Christians may be giving well “beyond their power” while for others it represents far less than is possible according to the prosperity the Lord gives.
I believe that as we study both Scripture and history, it is clear that the tithe was a 10% “ruler” (and “price tag”) that was used in the past by God’s people to show gratitude and thanksgiving to their God, as well as being a means to support a program through which God and his ways were made more visible. Today, as Christians, we do not have to tithe. Rather, our Lord wants us to give a generous percentage of our income to his kingdom work. We do this willingly, regularly and cheerfully.