It is only an exercise of the four virtues so that we as humans can achieve some sort of peace on our own through God's saving grace. To Augustine, humans seek an object of love they can't lose. The problem with that to humans is that humans can't provide that to other humans completely. Only God can and that in turn causes hostility among humans. The love of God, then, is the only way humans can completely satisfy all four virtues and have eternal peace.
Eternal peace is where faith, love, and hope are to be enjoyed, such as in The City of God.
In Book XIX, Augustinian social theory summarizes the principle of ordered harmony. This theory finds perfection in a mutual society that believes in God. Seemingly, war or hostility would not be a part of a Christian's life on earth. Augustine counters by indicating that war may be and is waged by God's commandment. To Augustine, waging war out of obedience to God is very different than to wage war for personal gain.