Philippians 3:20-21 remains in the present tense, but the teaching is essentially the same as I Corinthians 15:25-28. Verse 20 begins by asserting that we are now a colony of people whose real citizenship is in heaven. "Citizenship" indicates a fellowship or society all living under the same administration, but in this case, not living in the land of their citizenship. When we see this in context with His purpose, God is already drawing the church as a body into oneness with Him. Paul then goes on to assure us that by His power Christ will complete the process—even to transforming our bodies to be like His! What an awesome oneness to anticipate!
Paul began the section in verses 17-19 by contrasting two groups, and the difference between the two lies in the way each lives. He implies that those who are citizens of heaven are one, and they have a fellowship whose characteristics are opposite to "the enemies of the cross of Christ" (verse 18). They will end in destruction because they have "set their mind on earthly things" (verse 19). As a people living by sight, they are not in control of their flesh, their carnal nature.
Paul must have used "heaven" in verse 20 to emphasize how vast the difference between the two groups is. Heaven represents the unreachable to those whose minds are fixed upon goals limited to the earthly, carnal gratification of their senses. Though satisfying the self may be much easier at the moment, God says living that way will end in destruction.
Because we are reaching for something we cannot see, hear, smell, touch, or taste, the carnal mind perceives living by faith as wasting life on the unreachable or as living a daydream or fantasy. Why pursue something that never gives any immediate gratification? God, however, hastens to reassure us that He has the will and the power to bring us into this oneness with Him (verse 21).
John W. Ritenbaugh
All in All