How Good Must We Be To Get Into God's Heaven?

And escape eternal condemnation ...

The accuracy of your estimation of your own human holiness is a reflection of the accuracy in your understanding of the awful extent of the wretchedness of sin itself. Sin is so bad it sends the unredeemed sinner to a devil's hell separated eternally from our Creator, God. It was our sins which had no righteous remedy in the universe except the substitutionary, horrific and excruciating sacrifice of the very Son of God on that cruel cross. So when we judge ourselves, let us not use the flawed and false standard of the world, comparing our goodness to that of others, which Apostle Paul warned us about in  2Cor.10:12.    "For we dare not make ourselves of the number, or compare ourselves with some that commend themselves: but they, measuring themselves by themselves, and comparing themselves among themselves, are not wise."    Paul understood that the assumed goodness or badness of others, based on "appearances" was an inaccurate measurement.    "The LORD seeth not as man seeth; for man looketh on the outward appearance, but the LORD  looketh on the heart." 1 Sam.16:7.     God alone sees and knows the truth of us all and not a single soul qualifies, by their own goodness, for heaven and deliverance from eternal condemnation.  Jesus made that point clear in,     Matt.19:17 "There is none good but one, that it God...."  "For all have sinned and come short of the glory of God". 
Rom.3:23

Yes, many religions teach that we get to heaven by our good works, but God's word refutes that over and over again and cautions us that salvation is based on faith in Jesus and not in our good works.         
"Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified." Gal.2:16. 

A single sin, not covered by the blood of Jesus and unforgiven, if spread equally among the entire population of the earth, would render all unclean, unredeemed and is enough to send them all to hell. That is how bad sin is. But Jesus' death is more than sufficient to cleanse and sanctify the worst of sinners and give them the spiritual new birth experience through their faith and repentance. That is how powerful the life and death of Jesus is.

The only way to measure the full extent of the awfulness of sin is by its consequences of eternal punishment in an equally awful hell and the enormous price God paid for its forgiveness... the suffering and death of His sinless Son, Jesus.     
That is how bad sin is.       Let us keep that in mind when judging holiness or lack of it.

"For whosoever shall keep the whole law, and yet offend in one point, he is quilty of all. For he that said, Do not commit adultery, said also, Do not kill. Now if thou commit no adultery, yet it thou kill, thou art become a trangressor of the law." James 2:10-11.         
That dear friend is how bad a single sin is.

The good news is this ...    
"If we confess our sins, he is faithful and just to forgive us our sins, and to cleanse us from all unrighteousness." 1 John 1:9    And that is how powerful the faith of sincere repentance is.