Well first you would have the wrong impression for I never said that you can not sin, what I said is that you can not live in willful sin. Which there is a big difference according to the bible.
For the willful sinner is one who keeps doing the sin/sins without repentance, asking forgiveness, no remorse or conviction.
We Christians who backslide from time to time, will feel the conviction of the Holy Spirit and will be lead to repent and ask forgiveness of that sin.
There are two commandments that fulfill the law by following in them;
Matthew 22:37
Jesus said unto him, Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind.
Matthew 22:39
And the second is like unto it, Thou shalt love thy neighbour as thyself.
You can not obey either one of those commands if you don't follow the rest of what the Lord and Savior Jesus Christ said.
( And we are not held to the mosaic laws, Colossians 2:14 )
Here are some more of His commands, and then I will end it with a scripture where Jesus is explaining how somebody who believes in Him will be like;
Luke 13:3
I tell you, no! But unless you repent, you too will all perish.
Mark 16:16
He that believeth and is baptized shall be saved; but he that believeth not shall be damned.
Matthew 10:32-33
Whosoever therefore shall confess me before men, him will I confess also before my Father which is in heaven. But whosoever shall deny me before men, him will I also deny before my Father which is in heaven.
Matthew 28:16-20
The Great Commission
16 Then the eleven disciples went to Galilee, to the mountain where Jesus had told them to go. 17 When they saw him, they worshiped him; but some doubted. 18 Then Jesus came to them and said, “All authority in heaven and on earth has been given to me. 19 Therefore go and make disciples of all nations, baptizing them in the name of the Father and of the Son and of the Holy Spirit, 20 and teaching them to obey everything I have commanded you. And surely I am with you always, to the very end of the age.”
Luke 6:46-49
And why call ye me, Lord, Lord, and do not the things which I say? Whosoever cometh to me, and heareth my sayings, and doeth them, I will shew you to whom he is like: He is like a man which built an house, and digged deep, and laid the foundation on a rock: and when the flood arose, the stream beat vehemently upon that house, and could not shake it: for it was founded upon a rock. But he that heareth, and doeth not, is like a man that without a foundation built an house upon the earth; against which the stream did beat vehemently, and immediately it fell; and the ruin of that house was great.