Zacharias Ursinus was the primary author of the Heidelberg Catechism, which is considered substantially compatible with Westminster doctrine in the Presbyterian Church in America and elsewhere. Ursinus delivered lectures on his own catechism which were compiled in a book, Commentary on the Heidelberg Catechism. In the very beginning of those lectures he addresses the issue of why “doctrine” (theology) is important.

…This doctrine is the chief and most expressive mark of the true church, which God designs to be visible in the world and to be separated from the rest of mankind… (1 John 5.21; 2 Cor 6.17; 2 John 10; Isaiah 52.11; Rev 18.4)

God will that his church be separate and distinct from the world, for the following considerations: First, on account of his own glory; for, as he himself will not be joined with idols and devils, so he will not have his truth confounded with falsehood, and his church with her enemies, the children of the devil: but will have them carefully distinguished and separated. It would be reproachful to God to suppose that he would have and acknowledge as his children such as persecute him; yea, it would be blasphemy to make God the author of false doctrine and the defender of the wicked, for “what concord has Christ with Belial (2 Corinthians 6.14).

Secondly, on account of the consolation and salvation of his people; for it is necessary that the church should be visible in the world that the elect, scattered abroad among the whole human race, may know what society they ought to unite themselves, and that, being gathered into the church, they may enjoy this sure comfort, that they are members of that family in which God delights and that which he promises everlasting life. For it is the will of God that those who are to be saved, should be gathered into the church in this life. Out of the church there is no salvation.

COMMENT:

So not only is there (ordinarily) no salvation outside the church, to speak negatively, but the visible church is a “family” that delights God and to which God promises resurrection glory, to speak positively.

Question: So what happens to Reformed pastors in the PCA who agree with Zacharias Ursinus in their teaching and practice?

Answer: They get wrongly charged in the courts of the church and then vindicated.