It’s so helpful when the author provides a summary.

Prayer is the continuation of a conversation that God has started. He started it when he implanted knowledge of himself in every human being, when he spoke through the prophets and in his written Word, and especially when he called us to himself through the Holy Spirit sent into our hearts…The character of prayer is determined by the character of God we are reaching toward. The God to whom Christians pray is a triune God. We can pray because God is our loving Father, because Christ is our mediator giving us access to the throne of the universe, and because the Spirit himself indwells us.

Timothy J. Keller, Prayer: Experiencing Awe and Intimacy with God(United Kingdom: Hodder & Stoughton General Division, 2014), 83.