Brown's book definitely doesn't not try to push prayer on the basis of commandment. I like the title, "Approaching God." When we think about prayer, a lot of things flood into our mind, such as eyes closed, hands folded, "thees" and "thous", King James English--which is unfortunate, because they hinder what prayer is really all about, approaching God and not being at a distance from Him. Brown challenges the reader to re-conceive the idea of prayer in more approachable terms.
He relates a time when he felt self-righteous in prayer; because of this, he considered not praying at all. However, he said God told him that while He can deal with self-righteousness, He can't deal with distance. What is it about you, your Christianity, or your prayer life that tempts you to stop? Whatever it is, God loves you and will deal with you on the matter, but He wants you to keep coming to Him no matter what the imperfection.
Another important point in the book is that prayer can take many forms, because prayer is merely communicating with God. You might pray in a traditional way; you might pray in the car; you might choose to write out a prayer. It's all ok! The important point, again, is that you are actually going to God in some way.
Brown encourages people to not shoot for long hours of prayer if they can't do it. He suggests that you set a time limit of, say, 5 or 10 minutes, that you must finish before. Only set a higher time limit when you get to the point that you absolutely can't stay within your current time limit any longer.
These principles strike at some Christians' legalism regarding your "walk with God." I can imagine one such person chafing at the idea of setting a time limit for prayer. Well, you have to start from where you are at. The heart of Christian sanctification is continually coming to the Lord "just as I am, without one plea." If you are a five-minute-a-day praying Christian, that's great! If you need to pray more, that's the Lord's job to grow you into that. If you are a little selfish and irreverent in your prayers, don't worry! God will, in His time, make you more unselfish and fill you with the awe of His glory. It is not your job to force yourself into rules and roles that you will only fail at in your own strength.