The Greek noun aer (ἀήρ) refers to air or the lower atmosphere — the air we breathe, the space immediately surrounding the earth. In Greek cosmology, the aer was distinct from the higher, purer aither (ether); it was the lower, breathable atmosphere associated with clouds, mist, and the earthly realm.
In the New Testament, aer carries both mundane and theologically charged meaning. Practically, it describes the air that is beaten (1 Corinthians 9:26) or spoken into (1 Corinthians 14:9). Theologically, Paul calls Satan 'the ruler of the kingdom of the air' (Ephesians 2:2), and in 1 Thessalonians 4:17, believers will meet Christ 'in the air' at His return.
Two theologically significant uses of aer define Christian pneumatology and eschatology. First, Ephesians 2:2 describes Satan as 'the ruler of the kingdom of the air' — the spiritual forces of evil that inhabit the space between earth and heaven, influencing the 'sons of disobedience.' This is not a cosmological map but a statement of the pervasive spiritual opposition believers face.
Second, 1 Thessalonians 4:17 describes the rapture/resurrection gathering: 'we will be caught up together with them in the clouds to meet the Lord in the air.' The aer here is the meeting place between earth and heaven — the space where the ascended Christ will receive His people. What was once the domain of the enemy becomes the meeting point of divine redemption. Christ reclaims even the air.