Psa 95:10 Forty years long was I grieved with this generation, and said, It is a people that do err in their heart, and they have not known my ways: Psa 95:11 Unto whom I sware in my wrath that they should not enter into my rest.
Where do we find rest? We find it in God. I can say my life is very restful, because God is a God of peace and when we live for him, we live in peace. Why did not the children of Israel have peace? They did not know the ways of God because they refused to walk in the laws of God. Their problem was the same as our problem today, it was not a lack of knowledge but a lack of obedience.
Thats why God said in verses 6,7 Psa 95:6 O come, let us worship and bow down: let us kneel before the LORD our maker. Psa 95:7 For he is our God; and we are the people of his pasture, and the sheep of his hand. To day if ye will hear his voice. True rest comes not in just knowing facts about God but knowing God through obeying His Word.
Isa 26:3 Thou wilt keep him in perfect peace, whose mind is stayed on thee: because he trusteth in thee.