Is it permissible to offer condolences to Christians, and how would it be done if permissible?

It is permissible to offer condolences to non-Muslims upon death, to visit them when they are ill, and to console them in times of calamity, with the aim of inviting them to Islam and softening their hearts towards it. In the case of offering condolences, one should not pray for forgiveness or mercy for their deceased, due to the Almighty's saying: "It is not for the Prophet and those who have believed to ask forgiveness for idolaters, even if they were relatives." Rather, one should pray for them to have patience and remind them of Allah's sunnah (definition) (way) in His creation.