3:21 in the church. The “church” consisting of all born-again believers in Christ will be an eternal entity, even though also composed of many unique individuals. See, e.g., Hebrews 12:23, where it is called “the general assembly and church of the firstborn;” it is also called “the glorious church,” which is the bride of Christ (Ephesians 5:27; Revelation 21:9).
3:21 throughout all ages. There is evidently more than one age to come, but the succession of ages, however they may eventually be defined and revealed, will all be characterized by the “exceeding riches of His grace in His kindness toward us through Christ Jesus” (Ephesians 2:7).