Tithing was part of Old Testament Mosaic Law (Leviticus 27:30-33). Now, believers are under the Law of Grace because Jesus gave His life as the atoning sacrifice for our sins and in so doing, fulfilled the Law’s requirement for our sin (Matthew 5:17; John 3:16). But the New Testament provides guidelines for giving. Believers are to financially support those who work hard in the church (1 Timothy 5:17-18) and those whose main job is ministry and missionary work (1 Corinthians 9:14). This can include our local church and any Christian ministry doing God’s work. Additionally, we should financially help brothers and sisters in Christ who are in need (1 John 3:17-18). Ultimately, we should give as we have decided in our heart to, “not reluctantly or under compulsion, for God loves a cheerful giver” (2 Corinthians 9:7).
If we're not required to give a set amount, and if the New Testament tells us to provide for three categories of people, how do we decide how much to give to whom? The Bible doesn't say, so there is no hard and fast rule. Many preachers say to give ten percent to the church and give other donations to parachurch ministries and the needy, but again, that's more of a cultural guideline. As a member of a local body of believers, it's every church-goer's responsibility to make sure the needs of the church are met as the church practices good stewardship. In addition, we can spread Christ’s love to those outside the local church through giving. Part of developing spiritual maturity is learning to discern God's moral will for us through His word. As long as we understand that everything we have is a gift from God and He wishes us to use it to support the church, ministries, and the needy, we don't need rules to dictate specifics. Every believer should pray and ask God how they can give, and if God brings a need to our attention, we should do what we can to fulfill that need in cheerfulness, not compulsion or guilt.