The three books on Prayer: Merton's "New Seeds of Contemplation", Merton’s "Contemplative Prayer", Keller's "Prayer"

Merton's "New Seeds of Contemplation" might be kind of abstract to some people, especially to whom the culture/upbringing leaning towards practicality, although I agree breakthroughs are necessary. There's another book by Merton of title "Contemplative Prayer", which is a little bit more "instructional" & "definition-like". For something more protestant, Timothy Keller's title "Prayer" is good, yet it is more about conversational relationship with God, nevertheless with a contemplative sense. Actually I found Merton's "New Seeds of Contemplation" is pretty contemplatively conversational (with example as well): p.43-46 (end of chapter 6), his personal prayer is amazing!

Perhaps, one might need Keller's "Prayer" infrastructure and Merton's instructional & definition-like "Contemplative Prayer" to appreciate Merton's "New Seeds of Contemplation".