Hebrews 3:8

Harden not your hearts - Do not render the heart insensible to the divine voice and admonition. A hard heart is that where the conscience is seared and insensible; where truth makes no impression; where no religious effect is produced by afflictions; where preaching is listened to without interest; and where the mind is unaffected by the appeals of friends. The idea here is, that a refusal to listen to the voice of God is connected with a hardening of the heart. It is in two ways:

1. The very refusal to do this tends to harden it. And,

(2)In order to resist the appeals of God, people must resort to the means of “voluntarily” hardening the heart. This they do by setting themselves against the truth; by the excuses which they offer for not becoming Christians: by plunging into sin in order to avoid serious impressions; and by direct resistance of the Holy Spirit. No inconsiderable part of the efforts of sinners consists in endeavoring to produce insensibility in their minds to the truth and the appeals of God.

As in the provocation - Literally, “in the embittering” - ἐν τῶ παραπικρασμῶ en tō parapikrasmō. Then it means what embitters or provokes the mind - as disobedience. Here it refers to what they did to “embitter” the mind of God against them; that is to the course of conduct which was adopted to provoke him to wrath.

In the day of temptation - In the time of temptation - the word “day” being used here, as it is often, to denote an indefinite period, or “time” in general. The word “temptation” here refers to the various provocations by which they “tried” the patience of God. They rebelled against him; they did what put the divine patience and forbearance to a trial. It does not mean that they tempted God to do evil, but that his long-suffering was “tried” by their sins.

In the wilderness - The desert through which they passed. The word “wilderness” in the Scriptures commonly means a “desert;” see the notes at Matthew 3:1. “One provocation was in demanding bread at Sin; a second for want of water at Massah or Meribah; a third time at Sinai with the golden calf; a fourth time at Taberah for want of flesh; a fifth time at Kadesh when they refused to go up into Canaan, and the oath came that they should die in the wilderness. A like refusal may prevent us from entering into rest.” - Dr. John P. Wilson, Manuscript Notes.