17 And it may be thus understood, beloved brethren, that since the Lord commands and admonishes us even to love our enemies, and to pray even for those who persecute us, we should ask, moreover, for those who are still earth, and have not yet begun to be heavenly, that even in respect of these God's will should be done, which Christ accomplished in preserving and renewing humanity. For since the disciples are not now called by Him earth, but the salt of the earth, and the apostle designates the first man as being from the dust of the earth, but the second from heaven, we reasonably, who ought to be like God our Father, who makes His sun to rise upon the good and bad, and sends rain upon the just and the unjust, so pray and ask by the admonition of Christ as to make our prayer for the salvation of all men; that as in heaven— that is, in us by our faith— the will of God has been done, so that we might be of heaven; so also in earth — that is, in those who believe not — God's will may be done, that they who as yet are by their first birth of earth, may, being born of water and of the Spirit, begin to be of heaven.
Source: The Treatises of Cyprian (New Advent)