God is Holy and to receive us as His children into His family, we need to be holy too.
No person on earth is without sin and therefore we were unable to become His family.
Rom 3:23 for all have sinned and fall short of the glory of God,
Rom 6:23 For the wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord.
1John 1:10 If we say that we have not sinned, we make Him a liar, and His word is not in us.