In Protestant, Evangelical, Christian theology, especially in popular versions of the same, the charge of legalism is an accusation of ignorance of the Christian Gospel, or of unbelief. In that context, to apply the criticism of legalism to a theological position or religious attitude, implies that the accused has over-turned the Gospel of salvation through faith and new life in Jesus Christ, and has substituted for grace some principle of personal merit instead.
The Eastern Orthodox, for another example, reject the satisfaction theory of the atonement as legalistic. The satisfaction theory states that mankind's Original Sin violated God's law, resulting in all men being born guilty: an idea prevalent in the writings of Tertullian and Augustine of Hippo. Anselm formally developed the theory that the legal problem of guilt before the Law, required the legal solution of retribution, in order to achieve a just salvation. The solution was for God's son Jesus to willingly die on the Cross in place of humanity, thus allowing the legal penalty to be fully carried out, satisfying the justice of God, and thus clearing the way for mercy to be shown to sinners. The Eastern Orthodox charge that this theory is too dependent upon Roman legal concepts of retribution and justice.
In Roman Catholicism, good works are done in service to God and one's neighbor by faith working through love. In contrast, an excess of severity in the imposition of, or overly-scrupulous conformity to any rule of piety, may be charged with legalism.