I don't know about you, but when it comes to reading books that include a large number of lists of proof text references, my instinct is to skip the list and not bother to look up the relevant Bible passages. Reaching for a Bible and flicking through hundreds of pages to pursue multiple references to texts in Genesis, Numbers, Isaiah, Ezekiel, Hosea, Romans etc. is too much like hard work. However not looking up the relevant texts makes me feel guilty for being such a slacker. Besides, what we want from a theologian is theology that has been mined from the Bible, not simply a handy summary of Reformed doctrine that has little to do with the text of Scripture. John Frame rightly says,
after all has been said, theology really cannot do without proof-texts. Any theology that seeks accord with Scripture... has an obligation to show where it gets its scriptural warrant. It may not simply claim to be based on "general scriptural principles", it must show where Scripture teaches the doctrine in question. (The Doctrine of the Knowledge of God, John Frame, P&R, 1987, p. 197)
Bavinck includes many lists of Bible references in his Reformed Dogmatics. Currently I'm about a third of the way through Volume 2, God and Creation. I've just started Chapter 6, on The Holy Trinity. The theologian gives consideration to 'Old Testament seeds' of the doctrine of the Trinity. He carefully sets out his view that while the Old Testament may lack the fullness of the New Testament's revelation of the triune God, we may find "components that are of the highest significance for the doctrine of the Trinity" in the Old Testament (p. 261). Dozens of texts are adduced with regard to God's name, his work in creation by Word and Spirit and the angel of of Lord. Bavinck is a competent guide to the Scriptures to which he refers his readers. It is evident that he has given careful thought to the meaning of the passages cited. He is aware of differing exegetical approaches to the texts in question. Failure to pursue his lists of Bible verses would have deprived me of the wonder of encountering afresh God as Trinity in the pages of the Old Testament.
Anyway, the post's title promises an easy method of looking up proof texts. This is my labour-saving suggestion. Rather than arduously flicking your way through a printed copy of Holy Scripture, use an online Bible, such as BibleGateway.com. With the Passage Lookup feature, tap in the reference in abbreviated form. For example Hab 2:5-6. If you want to see a verse in its context, you can even click a button to bring up the whole chapter. It's much quicker (at least for me) to type abbreviated Bible references than leaf my way through a shiny black leather Bible with elegant gilt-edged pages.
If you have already figured out how to do this for yourself and were looking for an even more simple way of looking up proof texts, then sorry to disappoint you, but as far as I've discovered this is as easy as it gets. Indolence is the mother of invention, but it has its limits.