The grace of God is his unmerited favor, granted to believers in place of the wrath that their sins deserve. Sovereignly unconstrained by anything beyond himself, God lavishes grace through the sacrifice of Christ. In Packer’s terminology, grace is a way of speaking about all of God’s activity toward believers: “God operating in love toward people” (128).

Incarnation (which also appears in its adjectival form, incarnate) is the doctrine that the Son of God, one of the three divine persons of the Trinity, became a human being and was born as Jesus of Nazareth. This doctrine includes the idea that Jesus was both fully divine—sharing the divine nature in all its fullness with God the Father and the Holy Spirit—and also fully human, sharing in everything that makes human beings what they are.

In the Bible, jealousy is one of the attributes frequently ascribed to God. Packer notes that although jealousy is considered a vice in common parlance, there are circumstances in which it represents a proper and virtuous response—for instance, in the jealousy felt by a spouse whose partner is cheating on them. In a traditional Christian marriage, the romantic and sexual affections of one spouse belong to the other and no one else. In that context, the betrayed spouse quite properly feels jealousy for their partner’s affections. It is this form of jealousy that the Bible attributes to God, rooted in his love and desire for his covenant people, who had pledged themselves to him.

Justification, like adoption, is one of the benefits of salvation as presented in the Bible. The doctrine of justification refers to the way that Jesus Christ’s salvific death on behalf of Christians, taking their place and accepting the punishment for their sins upon himself, allows God to now regard Christians as righteous. The word indicates the process of being made just (or righteous), which is accomplished as a gift God grants, bringing them into a new status of favor and not counting their sins against them.

As with adoption and justification, this is also one of the benefits of salvation in Christian theology. Sanctification refers to the process of being made holy. Unlike justification, which is granted as a new status accorded in response to the once-for-all event of Jesus’s death on the cross, sanctification often takes the practical form of a process rather than a single event. Little by little, Christians are made ever more holy by the work of the Holy Spirit in their hearts, as they seek to know God more and to be conformed to the image of his Son.

In Christian theology, there is only one God, but God reveals himself as three eternal persons, constantly working together in a harmony of sovereign love to bring about the divine purpose. The three persons of the Godhead are God the Father, the Son (Jesus Christ), and the Holy Spirit, each co-equal in divinity and so intimately united in nature that they are both “three persons” and, at the same time, “one God.” This unity-within-threeness is referred to as the Trinity.