Territory that has been lost is territory that was once conquered by Christ. Isaiah 55 tells us exactly what this means. Ai is a classic illustration of losing territory. The churches of Revelation 2-3 had many wonderful things said about them, but they also had lost territory, just as the church of Ephesus had lost its first love.
This territory is easily lost and you can lose it in many ways. Throughout church history, we see that the church has lost territory. One area of loss relates to disobeying God's order. If God's order is not understood then territory is lost. For example, certain individuals can never get victory to build up the Body of Christ and flourish in the Word of God.
Imagine a Christian who has been granted grace, but loses territory by living under the Law. Think of a Christian who at one time had been flooded with joy and abounding in faith; however, soon he found himself with no joy and in bondage to fleshly drives.
The order of God is extremely important in establishing the redemptive hand of God upon the earth. Every place where our foot goes, we buy back from the enemy territory that has been lost ( Joshua 1:3). The order is that grace has the preeminence over the Law. The Spirit is our liberty through faith, and Christ has established His throne forever over all things. He has purchased territory and granted us the victory over it all. Now, we walk in the power of Redemption's order to appropriate and live in the land of promises.