This is the difference between positional holiness and practical holiness, God forgives and cleanses us from sin by His grace and from a grateful heart, we do what we can with His help to stay cleansed. One is not complete holiness without the other. There is a curse involved from sin that is mentioned in Malachi. The curse is brought on by our own selves. When the sins of the fathers are visited upon the children, it is like sin adding upon sin until the generation is cursed.
Sin has the result of exacting payment.
If it is not paid through repentance and forgiveness, it is paid in whatever result that the sin results in. In the case of divorce, it is in the destruction of the family, in the case of free sex, it is sexually transmitted diseases. I guess what I am saying is that much of the curse is in the absense of the Holy Spirit and the denial of blessing rather than any active aggression on the part of the Father. God is withholding His pleasure, He is cutting His people off. Rather than the curse coming directly from God, we are cursed with the curse itself that results in the natural course that the sin takes.