The worship at All Saints uses all three. First, kneeling is the most common posture in Scripture for prayer. Instead, one finds in the Bible a different posture for a very good reason. The bodily action of bending the knees in prayer puts form to our attitudes. They long to be clothed with flesh.
Prayer involves the whole person.
Worship should not just be a mental act, simply listening to a sermon. Kneeling, in many ways, represents what the whole of life should be. Second, sitting is an appropriate way of hearing the Word of God read and preached. You will notice that the Bible is read more in this type of service than in others. Many churches hardly ever read Scripture, which is a sad statement.