Not so. They are, in fact, entirely Biblical.
No where in the Bible does it list 7 deadly sins.
This is partially true. They are in the Bible, just not in a single list (they appear to have been compiled first by Pope Gregory I around AD 600):
I repeat man created that list,not God.Of course they are sins,but again I say God does not label only 7 sins as deadly.If you were to make a list today perhaps you would choose a different 7.Doesnt change the fact it is a fabrication of man.
These need to be read in context within the passage and overall NT. All sin is deadly in that, apart from Christ, it results in death.
I post the verses just after this one to illustrate why context is key.
Lust, is a sin. However, other things are mentioned as well that are to be avoided.
22Now flee from youthful lusts and pursue righteousness, faith, love and peace, with those who call on the Lord from a pure heart. 23But refuse foolish and ignorant speculations, knowing that they produce quarrels. 24The Lord’s bond-servant must not be quarrelsome, but be kind to all, able to teach, patient when wronged, 25with gentleness correcting those who are in opposition, if perhaps God may grant them repentance leading to the knowledge of the truth, 26and they may come to their senses and escape from the snare of the devil, having been held captive by him to do his will.
2 Timothy 2:22-26 NASB
The verese of Matthew 5:28 in context.
21“You have heard that the ancients were told, ‘YOU SHALL NOT COMMIT MURDER’ and ‘Whoever commits murder shall be liable to the court.’ 22“But I say to you that everyone who is angry with his brother shall be guilty before the court; and whoever says to his brother, ‘You good-for-nothing,’ shall be guilty before the supreme court; and whoever says, ‘You fool,’ shall be guilty enough to go into the fiery hell. 23“Therefore if you are presenting your offering at the altar, and there remember that your brother has something against you, 24leave your offering there before the altar and go; first be reconciled to your brother, and then come and present your offering. 25“Make friends quickly with your opponent at law while you are with him on the way, so that your opponent may not hand you over to the judge, and the judge to the officer, and you be thrown into prison. 26“Truly I say to you, you will not come out of there until you have paid up the last cent.
27“You have heard that it was said, ‘YOU SHALL NOT COMMIT ADULTERY’; 28but I say to you that everyone who looks at a woman with lust for her has already committed adultery with her in his heart.
29“If your right eye makes you stumble, tear it out and throw it from you; for it is better for you to lose one of the parts of your body, than for your whole body to be thrown into hell. 30“If your right hand makes you stumble, cut it off and throw it from you; for it is better for you to lose one of the parts of your body, than for your whole body to go into hell. 33“Again, you have heard that the ancients were told, ‘YOU SHALL NOT MAKE FALSE VOWS, BUT SHALL FULFILL YOUR VOWS TO THE LORD.’ 34“But I say to you, make no oath at all, either by heaven, for it is the throne of God, 35or by the earth, for it is the footstool of His feet, or by Jerusalem, for it is THE CITY OF THE GREAT KING. 36“Nor shall you make an oath by your head, for you cannot make one hair white or black. 37“But let your statement be, ‘Yes, yes’ or ‘No, no’; anything beyond these is of evil.
Matthew 5:21-37NASB
Very interesting that Jesus clarifies the definition of lust to include the mere thought of lust...not just the physical act itself. This illustrates that a single thought is in itself enough to cause sin.
Very surprised that murder wasn't on the list....considering we're talking the 7 "deadly sins."