Suppose you are really thirsty and I offer you a huge 64 oz glass of water. I'm sure you would be more than grateful and drink most of it right away.
But now let's suppose that before I give you the water I put a drop of arsenic in it. Would you drink it now?
Of course not. Even though it is a huge glass of water that one little drop of arsenic ruins the whole thing causing it to be undrinkable.
That is the way it is with sin. Just one sin in our whole life causes us to be unworthy and keeps us from Heaven. God's standard to get into Heaven is to be perfect and none of us are perfect.
Be ye therefore perfect even as my Father in Heaven is perfect. Matthew 5:48
That is why we need Jesus. He lived the perfect life for us and paid for our sins on the cross.