There are many places where the Bible seems to propose contradictory teachings. The key many times is to read the verses in context as well as understanding them in isolation. Also, understand that scripture is the child of Tradition, and not the other way around.
(Also, Countrychurch, you were just using a turn of phrase, not implying that God... One of the things about all language is its absolute insufficiency to express the supernatural.)
In the first instance, Our Lord Jesus Christ is telling us that prayer is an outgrowth of Faith. Some people pray as though everything depends on them and their prayers, or that God has set some "quota" that they must reach before He will answer a prayer. In the first example Our Lord is counseling us to have peace of soul and confidence in God. God can do all things and will do them in His own good "time".
In the second instance, Our Lord is telling us that our prayer must be constant. That is, we must persevere. "He who perseveres to the end will be saved."
The practical application is this:
For example, praying for the triumph of the Immaculate Heart at Fatima...
In instance #1, Our Lord would counsel against praying the rosary continuously to the neglect of other duties. We should pray our rosary devoutly (at least 5 decades, as requested by Our Lady, but the whole 15 decades if we have the time, for we should never be satisfied with the minimum.) and then be satisfied and at peace we have done our daily prayers, and serenely go about our other duties.
In instance #2, let's say we have done the five Saturdays as requested by Our Lady of Fatima. Well, let us keep doing them. Let us also make sure we persevere in saying the rosary. We should never be satisfied with our "spiritual accomplishments" but ever striving for perfection.
Advancing in the spiritual life is like climbing a mountain. The higher you go, the smaller you feel. The more you can see to the horizon, the more you realize there is a whole lot more you can see.
Imagine your dog doing algebra... Trying to understand the ways of God is harder for us to do than for a dog to do algebra...