If anyone comes to you and does not bring this teaching, do not receive him into your house or give him any greeting, for whoever greets him takes part in his wicked works.
2 John 10-11, ESV

To express unity of faith with false teachers is to partake in their works—false teachings. In agreement with the Brief Statement once held by the LCMS, the theses on fellowship adopted by the Wisconsin Evangelical Lutheran Synod teaches that “Those who practice church fellowship with persistent errorists are partakers of their evil deeds. 2 Jn 11.”

• Paul, in unity with John, warned that false teachers arise because they have the support of “itching ears” (2 Timothy 4:3-4).
• That fellowship is a sharing of deeds is taught not only by the apostles but also by our Lord, who said whoever supports a prophet will receive a prophet’s reward, etc. (Matthew 10:41).

In short, partaking in joint expressions of Christian unity by its nature is fellowship—sharing—in one another’s doctrine. A joint confession of faith is necessarily a confession of a joint faith.

The theses continue, “His clear injunction (also flowing out of love) to avoid those who adhere to false doctrine and practice and all who make themselves partakers of their evil deeds.”

• Those sharing in the evil deed of causing division must be denied fellowship (Romans 16:17-18).

In other words, to condone sharing in that is to become a partaker. What about those who by their offerings, joint communion, church membership, and other expressions of a common faith take their stand with a leader making a common confession with false teachers in their name? They thereby take part in the leader’s work of false teaching:

If anyone comes to you and does not bring this teaching, do not receive him into your house or give him any greeting, for whoever greets him takes part in his wicked works.
2 John 10-11, ESV