Jamieson, Fausset and Brown on Hebrews 5:11

11. Here he digresses to complain of the low spiritual attainments of the Palestinian Christians and to warn them of the danger of falling from light once enjoyed; at the same time encouraging them by God's faithfulness to persevere. At He 6:20 he resumes the comparison of Christ to Melchisedec.

hard to be uttered--rather as Greek, "hard of interpretation to speak." Hard for me to state intelligibly to you owing to your dulness about spiritual things. Hence, instead of saying many things, he writes in comparatively few words (He 13:22). In the "we," Paul, as usual, includes Timothy with himself in addressing them.

ye are--Greek, "ye have become dull" (the Greek, by derivation, means hard to move): this implies that once, when first "enlightened," they were earnest and zealous, but had become dull. That the Hebrew believers AT Jerusalem were dull in spiritual things, and legal in spirit, appears from Ac 21:20-24, where James and the elders expressly say of the "thousands of Jews which believe," that "they are all zealous of the law"; this was at Paul's last visit to Jerusalem, after which this Epistle seems to have been written (see on He 5:12, on "for the time").