The word communicate in the King James version means "to share"—as the New King James has it—"to associate, partake, participate, distribute; to impart." We who are being taught are to impart to those who are teaching. Adam Clark, commenting on the phrase "communicate to him that teaches," remarks:
Contribute to the support of the man who has dedicated himself to teach the work of the ministry, and who gives up his time and his life to preach the gospel. We do not expect the schoolmaster to give up his time to teach our children the alphabet without being paid for it, and can we suppose that it is just for any person to sit under the preaching of the gospel in order to grow wise unto salvation by it and not contribute to the support of the spiritual teacher? It is unjust!
The Expositor's Bible Commentary's entry on Galatians 6:6-10 reads:
Three uses of money are mentioned: 1. the support of the teacher in a Christian congregation [first tithe]; 2. the use of money to build up the Spirit rather than to feed the flesh [This is an arbitrary categorization. I would dare say, however, this is a perfectly lawful use of the second tithe]; 3. the spending of money to help others, particularly Christians [the third tithe fund]. The reference to the one who is taught in the word does not imply a fully developed oral instruction system, such as prevailed in the church later on, but it does point to a class of paid teachers at a surprisingly early date. Paul's policy was apparently to preach the gospel without receiving money, preferring to earn his living as a tent maker. But this was pioneer work. As soon as possible he seemed to have established a more fixed structure.
The apostle Paul did not want anyone to come and say to the Corinthians or to anyone with whom he was working, "You know, he is just teaching you so he can get your tithes. He just wants your money!" Paul did not want this.
In I Corinthians 8, Paul says, "I would not eat meat at all if it were to offend anyone. I would not eat meat for the rest of my life." This is the same principle in which he is instructing the Galatian brethren. Paul did not have an office to run, a car to maintain, or things of the administrative sort we usually have today. The point is that Paul would not accept monetary compensation in order not to offend anyone.