So what is sin?
Sin is basically anything that is contrary to God's will. The Bible details many examples of sin. But this may help you: How man times must you rob someone to be called a robber? Or how many times must you kill someone to be a killer? Or how many times must you commit adultery to be an adulterer?
The answer is ONCE!
In Revelation 21:8 it reads, "But the fearful, and unbelieving, and the abominable, and murderers, and whoremongers, and sorcerers, and idolaters, and all liars, shall have their part in the lake which burneth with fire and brimstone: which is the second death."
Did you notice "all liars?" Back to our earlier question, How many lies must you tell to be a liar? Only One!
So even a small lie is sin. And sin will not be allowed into heaven.