Final answer:
According to Ephesians 3, God's plan had always been Christ and the Church, made up of Jews and Gentiles from every nation, saved by grace through faith.
Step-by-step explanation:
The correct answer is A) Ephesians 3.
In Ephesians 3, the apostle Paul describes God's plan as the mystery now revealed. He explains that God's plan had always been Christ and the Church, made up of Jews and Gentiles from every nation, saved by grace through faith, and marked by the indwelling Holy Spirit as the one people of God.
Paul's teachings in Ephesians emphasize the inclusive nature of Christianity, where membership is not limited to Jews but open to people from all nations. This understanding of the universal salvation offered by Christ and the expansion of the Church to include Gentiles was an important development in early Christianity.
Overall, Ephesians 3 highlights the unity and inclusivity of the Church, bringing together Jews and Gentiles in a common faith.