Many Christians do that? Chapter and verse please. There are genuine Christians and there are "nominal" Christians. There are genuine believers and there are make believers mixed together throughout various churches and on various Christian forum sites.
Elsewhere in the book of Hebrews 4:1-2, we read - For indeed the gospel was preached to US as well as to THEM; but the word which THEY heard did not profit THEM, not being mixed with faith in THOSE who heard it.
For WE who have believed do enter that rest, as He has said: "So I swore in My wrath, 'They shall not enter My rest," although the works were finished from the foundation of the world.
Obviously, not all of these Hebrews were genuine believers. *Notice that verses 2-3 makes a distinction between US who have BELIEVED and do enter that rest and THEM who heard the word but did not mix faith with what they heard and will not enter that rest because of UNBELIEF.