In Western Christian beliefs, grace is God's favor, and a "share in the divine life of God". It is a spontaneous gift from God – "generous, free and totally unexpected and undeserved" – that cannot be earned. In the Eastern Orthodox Church, grace is the uncreated energies of God. Among Eastern Christians generally, grace is considered to be the partaking of the divine nature described in 2 Peter 1:4 and grace is the working of God himself, not a created substance of any kind that can be treated like a commodity.

As an attribute of God, grace manifests most in the salvation of sinners, and Western Christianity holds that the initiative in the relationship of grace between God and an individual is always on the side of God.

The question of the means of grace has been called "the watershed that divides Catholicism from Protestantism, Calvinism from Arminianism, modern theological liberalism from theological conservatism." The Catholic Church holds that it is because of the action of Christ and the Holy Spirit in transforming into the divine life what is subjected to God's power that "the sacraments confer the grace they signify": "the power of Christ and his Spirit acts in and through [each sacrament], independently of the personal holiness of the minister. Nevertheless, the fruits of the sacraments also depend on the disposition of the one who receives them."

Catholics, Eastern Orthodox and Protestants agree that grace is a gift from God, as in Ephesians 2:8: "For by grace you have been saved through faith, and that not of yourselves; it is the gift of God." Lutherans hold that the means of grace are "the gospel in Word and sacraments." That the sacraments are means of grace is also the teaching of John Wesley, who described the Eucharist as "the grand channel whereby the grace of his Spirit was conveyed to the souls of all the children of God".

Calvinists emphasize "the utter helplessness of people apart from grace." But God reaches out with "first grace" or "prevenient grace". The Calvinist doctrine known as irresistible grace states that, since all persons are by nature spiritually dead, no one desires to accept this grace until God spiritually enlivens them by means of regeneration. God regenerates only individuals whom he has predestined to salvation. Arminians understand the grace of God as cooperating with one's free will in order to bring an individual to salvation. According to Evangelical theologian Charles C. Ryrie, modern liberal theology "gives an exaggerated place to the abilities of people to decide their own fate and to effect their own salvation entirely apart from God's grace."

Grace is the English translation of the Greek χάρις (charis) meaning "that which brings delight, joy, happiness, or good fortune."

The Septuagint translates as χάρις the Hebrew word חֵ֖ן (ẖen) as found in Genesis 6:8 to describe why God saved Noah from the flood. The Old Testament use of the word includes the concept that those showing favor do gracious deeds, or acts of grace, such as being kind to the poor and showing generosity. Descriptions of God's graciousness abound in the Torah/Pentateuch, for example in Deuteronomy 7:8 and Numbers 6:24–27. In the Psalms, examples of God's grace include teaching the Law (Psalm 119:29) and answering prayers (Psalm 27:7). Another example of God's grace appears in Psalm 85, a prayer for restoration, forgiveness, and the grace and mercy of God to bring about new life following the Exile.

In the definition of the Catechism of the Catholic Church, "grace is favour, the free and undeserved help that God gives us to respond to his call to become children of God, adoptive sons, partakers of the divine nature and of eternal life". Grace is a participation in the life of God, which is poured unearned into human beings, whom it heals of sin and sanctifies.