There are lots of examples of mortal sin in the bible.
Galatians 5:29 “Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, 20 Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, 21 Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God.”
St. Paul had to warn these believers at least twice, that if they continued in these sins they would not enter heaven.
But, since everyone sins, why didn’t he say that no one would inherit the kingdom?
Because no all sins are mortal sins. Only mortal sins, deadly sins, exclude us from heaven
And in Galatians 3:26, he says, “For ye are all the children of God by faith in Christ Jesus. 27 For as many of you as have been baptized into Christ have put on Christ”
Therefore they all had faith, but not all were going to heaven. Faith alone is not enough. They had to repent and quit giving into mortal sin to enter heaven.