Here’s how Schreiner summaries his answer (p. 221):
Even though tithing is not mandated, there is no call in the New Testament to hoard one’s possessions or to live selfishly. Believers are commanded to support those who proclaim the gospel (Matt. 10:10; Luke 10:7; 1 Cor. 9:6–14; 1 Tim. 5:17–18). Those who are blessed with wealth are to enjoy the good things God has given them, but they are also to be generous to those in need (1 Tim. 6:17–19). The New Testament clearly teaches that wealth is dangerous because it can seduce us so that we stray from the Lord. God is to be our treasure, and hence believers are to give generously and freely. For most believers in the West, that means giving more than a tithe. Still, the tithe itself is not mandated by Scripture, and Scripture is our rule and authority rather than a tradition that requires believers to tithe.
Related: What We Should Do with Our Money (esp. the resources at the bottom of the post)