From the very beginning of the church, sharing was one of the marks of Christian experience (Acts 2:41–47). The Greek word, koinonia, simply means “to have in common,” and refers to our common fellowship in Christ (Gal. 2:9), our common faith (Jude 3), and even our sharing in the sufferings of Christ (Phil. 3:10). But often in the New Testament, koinonia refers to the sharing of material blessings with one another (Acts 2:42; 2 Cor. 8:4). It is this that Paul has in mind in these verses.
Most of us are naturally selfish and must overcome this fault as we mature. Paul shows how grace frees us to share financially with others. He begins in verse 6 with a precept on generosity. He says that we must share our financial resources with our spiritual leaders. When a pastor-teacher shares instruction, then the student is to reciprocate by sharing all good things. Pastoring and teaching is time-consuming and is sometimes a thankless job. Let us share our appreciation for these pastors and teachers.
But we must realize the spiritual principle that lies behind this precept. God does not command believers to give simply that pastors and teachers (and missionaries, Phil. 4:10–19) might have their material needs met, but that the givers might get a greater blessing (Gal. 6:7–8). The basic principle of sowing and reaping is found throughout the entire Bible. God has ordained that we reap what we sow. But God has also told us to be careful where we sow, and it is this principle that Paul deals with here. He looks on our material possessions as seed, and He sees two possible kinds of soil: the flesh and the Spirit. We can use our material goods to promote the flesh, or to promote the things of the Spirit. But once we have finished sowing, we cannot change the harvest.