Answer: Because you are not good enough, through Adam sin and the knowledge of good and evil has been passed down to all mankind.
Now this may seem like a harsh and depressing reply, so let me explain further with scripture.
(Romans 3:10-12 ESV) as it is written: “None is righteous, no, not one no one understands no one seeks for God. All have turned aside together they have become worthless no one does good, not even one.”
(Isaiah 64:6 ESV) We have all become like one who is unclean, and all our righteous deeds are like a polluted garment. We all fade like a leaf, and our iniquities, like the wind, take us away.
(Romans 3:23 ESV) for all have sinned and fall short of the glory of God,
All of us have sinned and fallen short of the glory of God, thus we are not good. To be good enough for God we must be good.
(Mark 10:18 ESV) And Jesus said to him, “Why do you call me good? No one is good except God alone.
Only God is good.
(Mark 10:26-27 ESV) And they were exceedingly astonished, and said to him, “Then who can be saved?” Jesus looked at them and said, “With man it is impossible, but not with God. For all things are possible with God.”
(John 3:16 ESV) “For God so loved the world, that he gave his only Son, that whoever believes in him should not perish but have eternal life.
(Romans 5:8 ESV) but God shows his love for us in that while we were still sinners, Christ died for us.
Even though we are not good enough God sent His son Jesus, who was good, to make us good through Him.
(Ephesians 2:4-5 ESV) But God, being rich in mercy, because of the great love with which he loved us, even when we were dead in our trespasses, made us alive together with Christ—by grace you have been saved—
(2 Corinthians 5:17 ESV) Therefore, if anyone is in Christ, he is a new creation. The old has passed away; behold, the new has come.
Only in Christ are we good enough, for He makes us new, erasing the sin from us.
(Romans 8:1 ESV) There is therefore now no condemnation for those who are in Christ Jesus.
(John 10:10 ESV) The thief comes only to steal and kill and destroy. I came that they may have life and have it abundantly.
In Jesus you no longer need to feel inadequate for He is your rightiousness and justification. Christ's goodness is imputed (credited to our account) on us. Through Repentance and Faith in Him, you can have life to the full with out the condemnation of sin.