The word "us" refers to Paul, the Ephesian church, and all believers in Christ. Alternate translation: "God planned long ago to adopt us" (See: [[rc://en/ta/man/translate/figs-inclusive]])
Here "adoption" refers to becoming part of God's family. Here the word "sons" refers to males and females. Alternate translation: "to be adopted as his children" (See: [[rc://en/ta/man/translate/figs-gendernotations]])