When the Church prays "our Father who art in heaven," she is professing that we are the People of God, already seated "with him in the heavenly places in Christ Jesus" and "hidden with Christ in God;" yet at the same time, "here indeed we groan, and long to put on our heavenly dwelling."
[Christians] are in the flesh, but do not live according to the flesh. They spend their lives on earth, but are citizens of heaven.
Source: Catechism of the Catholic Church (Vatican.va)