Be sure to check out Mark Nanos' article, "'Callused,' Not 'Hardened': Paul's Revelation of Temporary Protection Until All Israel Can Be Healed", in which he argues for a more precise treatment of the term πώρωσις in Rom 11:7,25. From the essay:
"Paul does not use σκληρός or cognates to describe the state of Israelites; instead, he uses πώρωσις in 11:25 (and as a passive verb in v. 7: ἐπωρώθησαν) to describe the state of some (many) of his fellow Israelites. Πώρωσις (verb πωρόω) refers to a "callus" (verb: to callus) not to "hardness" per se... The formation of a callus -- which involves a process of hardening, to be sure -- is to offer protection so that the injured area can sustain life. It promotes healing of broken bones or wounds, not harm or destruction, or metaphorical resistance. It creates an area less sensitive to touch, but that too is a positive feature versus the continuation of the sensation of pain where the injury occurred." (pp 3-4)I would urge even more strongly than Nanos does (see p 31), however, that the context of Rom 11:1-10 doesn't adequately signal this more positive understanding of Israel's current state in verse 7 -- just the opposite, in fact. It's only when Paul turns to explain that "not all is as seems" in Rom 11:11-32, that we indeed appreciate "callused" as better suited to what's being depicted in verse 25.