“We have seen that there are different types of prayer and each has its own particular principles. The prayer of persistence is a clear example. Unlike the prayer of faith, this is offered repeatedly until the breakthrough is experienced.
It is vitally important, as in the parable in Luke 18:1-8, not to give up when our prayers seem to go unanswered. We must press on, for the Judge who is willing and good will surely answer our cause.
In Revelation 5:8 & 8:4, the prayers of the saints rise up like incense before God. This is an encouragement to keep praying, for our prayer might be the last prayer required before the bowls are full and the promise of Hosea 10:12 is obtained.” (From Colin Dyr, Effective prayer, p. 136).