What has just been said should not lead any one to regard religious unionism (syncretism, Unionismus., Religionsmengerei) as permissible, much less as laudable. The words "with charity toward all" apply indeed to all men, for Christians are commanded to love all men, Matt. 22, 39; 5, 44; 1 John 3, 17. 18; but they do not mean that Christians should countenance false prophets and their errors, Matt. 7, 15; Gal. 1, 8. 9. The direction of Scripture with regard to this point is both clear and emphatic, Rom. 16, 17; Gal. 5, 9; 2 John 10. 11; Titus 3, 9-11; 1 Tim. 1, 3-7; 2 Cor. 6, 14-18.
To the objection that religious unionism may be justified both because of the principle of Christian charity, Rom. 13, 10; 1 Cor. 13, 7, and in view of Christ's earnest prayer that all believers may be one, John 17, 20. 21, we reply -
a) That it is indeed only a caricature of Christian love to permit any one to grope in spiritual darkness and to endanger his soul's salvation, 2 Cor. 5, 13-15; 1 Cor. 9, 22. 23; 2 Cor. 6, 3-10, so that religious unionism, which in the last analysis is carnal indifferentism, really ignores true Christian love both toward God (faithfulness to His Word) and toward the neighbor (conscientious interest in his avowal of the divine truth);
b) That the unity which the Holy Ghost Himself works through the Word is the unity of faith, John 17, 17. 20. 21. 25. 26; Eph. 4, 3-6; 1 Cor. 1, 10, which Christians must foster by witnessing to the truth.
True unity of faith is indeed commanded by God, 1 Cor. 1, 10, and all Christian believers should therefore do all in their power to effect it. But this unity, which is of the Spirit, is neither established nor furthered by carnal indifferentism and toleration of error, 2 Cor. 6, 14-18; 1 Kings 18, 21. 22. 40.
The peril that lurks in religious unionism is that by an unfortunate consistency in the profession of falsehood one error always produces another. So also carnal indifferentism toward one doctrine is bound to produce carnal indifferentism towards others. Luther says St. L., XVII, 1180: "Whoever regards his doctrine, faith, and confession as true, right, and certain cannot stand in one stall with others that teach or favor false doctrine." Cp. XVIII, 1996.
The contention of modern rationalistic theologians that the "various theological tendencies" (denominational divisions) are intended by God is neither Scriptural nor reasonable.