This passage in Hebrews 5:11-14 is not only transitional to the 3rd major warning in Hebrews, but it is also foundational for a correct understanding of one of the most difficult passages in the Book. These verses are clearly addressed to believers who have become "dull of hearing" which leads to the loss of blessings associated with their salvation in Hebrews 6:1-8. These verses -- which can be summarized by the expression 'use it or lose it' -- can also be outlined as follows.
Transition: "Concerning him..." (i.e. Melchizedek) -- connects this segment to the previous passage in Hebrews 5:5-10 (v.11a)
I. Two reasons why the concept of Melchizedek's relationship to Jesus our great high priest is "hard to explain" (v.11)
A. Because there's just so "much" content to be communicated and understood (v.11b)
B. But the primary reason is because these Hebrew Christians have simply become "dull of hearing" and cannot understand (v.11c)
Transition: The big question to be explored in the segment to follow in verses 12-14 is -- WHY?
II. The far-reaching ramifications of becoming "dull of hearing" (vv.12-14)
A. These Jewish believers should be teachers by now, but instead they've even forgotten the fundamentals of the faith (v.12a)
(In other words...'Use it or lose it!')
B. An illustration everyone can identify with: these believers are like immature babies who need milk, not solid food (12b-14a)
1. They have "come to need milk" -- i.e. their spiritual growth has been stunted, or even regressed (v.12b)
2. As a result they are not "accustomed to the word of righteousness" -- They are not used to hearing teaching about how saved people who have been declared righteous by faith should live a righteous lifestyle -- and they remain babes in Christ (v.13)
3. In contrast, solid food -- i.e. teaching beyond the basic principles of the Gospel -- is for maturing believers (v.14a)
III. Finally the question of what makes the difference between mature and immature believers is explored (v.14b)
A. 'Practice makes perfect' - or at least moves one in the direction of completeness in their faith (v.14b)
B. "Practice" is what trains the senses to "discern" (i.e. know) the difference between "good and evil" -- the "word of righteousness