J. W. Rogerson 
The Art of Biblical Prayer [EPUB ebook] 

Prayer’ is a word that is used in a number of different ways. For many people it means essentially petition or intercession. Understood in this way, prayer easily becomes an 'extra’ – something that is not essential to Christianity, but that some Christians do sometimes, as the need arises. This book aims to show that prayer should be understood as inseparable from Christianity, in the sense that to practise Christianity is to practise prayer and vice versa.