Ecumenicity is yet another chief characteristic of the Wauwatosa Gospel. This principle of the Wauwatosa Gospel, Joh. Ph. Koehler wrote, is in direct contrast to the slothful, dogmatic ideas of unionism and isolationism. It is not a matter of the mind, but of the heart and is worked only by the Holy Spirit. In his “Legalism Among Us,” The Wauwatosa Theology, Vol. II (Milwaukee: Northwestern Publishing House, 1999), Koehler writes:
“The ecumenical spirit accordingly does not consist in our having a doctrine of the invisible church. This is a great gift from God. But we make it into something external, if pondering stops here. Again, however, the ecumenical spirit also does not consist in the unprincipled overlooking of the inner differences, which certainly must divide, if one wants to remain truthful. Such indifference is also of an external, superficial kind.
“By ecumenicity of evangelical preaching I understand that one always fosters the sensibility for the one true invisible church, the communion of those who truly believe in the Lord Jesus, as opposed to the partisanship of the various concrete church bodies in the world who claim for themselves that they are the true visible church. The ecumenical spirit is something internal which belongs to the individual person through the Holy Spirit” (247).