3:8

do not harden your hearts: The word picture of hardening one’s heart (or neck) was used in the Hebrew Scriptures with reference to individuals who refused to trust in Jehovah and obey him. (2Ki 17:14, ftn.; Ne 9:16, 17, ftns.; Pr 28:14; Jer 17:23, ftn.; Zec 7:12) When a person continually refuses to obey Jehovah, his heart gradually becomes hardened, that is, unfeeling and unresponsive to God’s will. (Ex 8:15, 32; 9:34) Paul exhorts the Hebrew Christians to develop a sensitive heart, that is, to “listen to” God’s voice. (Heb 3:7, 12-15) Listening would include obeying, not merely hearing, what God says. By doing so, the Hebrew Christians would prevent their sensitive hearts from becoming calloused and stubborn.​—De 10:16.

as on the occasion of provoking to bitter anger, as in the day of testing: The verse quoted here, Ps 95:8, refers to what happened while Israel was in the wilderness. At Rephidim, the Israelites murmured about the lack of water, so Moses named the place Meribah (meaning “Quarreling”) and Massah (meaning “Testing; Trial”). (Ex 17:1-7; see ftns. on v. 7; De 6:16; 9:22; see App. B3.) This was not the only occasion when the Israelites murmured. (Nu 14:11, 22, 23) For example, they complained about the lack of water at another place called Meribah, this one in the Kadesh area. (Nu 20:1-13) In the Greek Septuagint translation of Ps 95:8 (94:8, LXX), which Paul quotes here, the Hebrew place names are not transliterated. Instead, “Meribah” and “Massah” are translated with Greek expressions that can respectively be rendered “the occasion of provoking to bitter anger” and “testing.” This wording may suggest that Paul is referring not just to a specific incident but to the entire faithless course of the Israelites during their 40 years of wandering in the wilderness.​—Nu 32:13; Heb 3:9.