This fascinating phrase (actually, the Greek simply says "in the heavenlies") is found only in the Ephesian epistle where it occurs five times. That it does mean heavenly places, rather than "heavenly things," is evident from our text. Christ in His physical resurrection body is now in a particular place, and that place is where He is seated at the right hand of the throne of God.
In principle now--and ultimately in actuality--we also have been made to "sit together in heavenly places in Christ Jesus" (2:6). In the meantime, however, we must also struggle with the demonic powers who still, like Satan, have access to God's presence to accuse us of sin when we yield to their inducements. "For we wrestle not against flesh and blood, but against principalities, against powers, against the rulers of the darkness of this world, against spiritual wickedness in high places |actually the same phrase, 'heavenly places'|" (6:12).
And when, by the grace of God and the indwelling presence of God's Holy Spirit, we are victorious in this conflict, it becomes a glorious demonstration throughout heaven, to fallen and unfallen angels alike, that Christ's salvation is genuine and truly works in our lives. All of this is "to the intent that now unto the principalities and powers in heavenly places might be known by the church the manifold wisdom of God" (3:10).
No wonder, with all these glorious events taking place in heaven, the apostle Paul introduces this epistle with a doxology! "Blessed be the God and Father of our Lord Jesus Christ, who hath blessed us with all spiritual blessings in heavenly places in Christ" (1:3). HMM