Q. May one attend a service at a church, e.g. for a funeral?
A. Harmonious relationships with gentiles are part of the ethic of darkei shalom, “the ways of peace”.
Thus the sages say, “We support the poor of the gentiles as we support the Jewish poor; we visit the sick of the gentiles as we visit the Jewish sick; we bury the dead of the gentiles as we bury the Jewish dead” (Gittin 61a).
Nonetheless a Jew should not attend a funeral or other service in a church unless it is absolutely necessary.
The religious symbols, theology and liturgy of the church are obviously incompatible with Judaism, and whilst there is a great deal that is possible and practicable in inter-community dialogue and co-operation, we cannot compromise our conscience or convictions.