In his biblical theology of the New Testament lectures Gordon Fee proposes a unifying principle that must include at least four items:

1. The church as an eschatological community, who form the new covenant people of God.
2. The eschatological framework of their existence and thinking.
3. Their being constituted by God’s eschatological salvation effected through the death and resurrection of Christ.
4. Their focus on Jesus as Messiah, Lord, Son of God.

Or to put in another way:

• Foundation: A gracious and merciful God, who is full of love toward all.
• Framework: Eschatological existence as already/not yet.
• Focus: Jesus, the Son of God, who as God’s suffering servant Messiah effected eschatological salvation for humanity through his death and resurrection, and is now the exalted Lord and coming King.
• Fruit: The church as an eschatological community, who, constituted by Christ’s death and the gift of the Spirit, and thus restored into God’s likeness, form His new covenant people.

Fee puts this together in a condensed summary:

Through the death and resurrection of his Son Jesus, our Lord, a gracious and loving God has effected eschatological salvation for his new covenant people, the church, who now, as they await Christ’s coming, live the life of the future by the power of the Spirit.