If this comment by Neibuhr is right, does it mean that religion is at times of necessity immoral, and that God is therefore also immoral (morality, of course, not being the same thing as holiness)?

It must be immediately evident that every religious assurance of grace and every concomitant emotion of contrition contain certain perils to a socio-moral passion which strives to correct the imperfections of society and which must count upon impatient and, on the whole, self-righteous men to perform the task. The knowledge of the equal sinfulness of all human nature is not completely compatible with a social purpose which sets the relatively good ideal against the relative injustices of society. This incompatibility between the temper of classical religion and strenuous morality proves that the relation of religion and morality is never simple and is not exhausted in their mutual support of each other on certain levels. In certain areas the conflict is permanent; but its permanency does not justify the suppression of one in favour of the other.
All men who live with any degree of serenity live by some assurance of grace. In every life there must at least be times and seasons when the good is felt as a present possession and not as a far-off goal.

– Reinhold Niebuhr. Reflections on the end of an era. (1934) p.284.