Many misunderstand grace thinking that once they have been 'saved' by faith in Jesus they have come 'under the blood' and sin is covered automatically. Certainly there is no condemnation to those who are in Christ (Ro.8:1). But it doesn't mean that because we are under grace sin has no consequences on our life. If we sin after we have come under grace the first thing we ought to do is to confess it and receive forgiveness (1Jn.1:9). If there is sin that we are aware of but we don't deal with it in this way, it will come in the way of our fellowship with God (Ps.66:18). Confessing it helps us to maintain our relationship with God. But there is another consequence of sin that we may not usually think of. That is the damage that sin does to us personally and to others around us.
God told Adam and Eve that if they disobeyed Him by eating the forbidden fruit they would 'die' (Ge.2:17). This death pertains mainly to the breaking of relationship with God. But the other aspect of this death is the corruption that comes to the one who sins. God makes it very clear that if we do anything to please the sinful desires in our flesh we would 'reap corruption' (Ga.6:7,8). Everything sinful we do will affect us in our body, soul and spirit. We won't be the same as before. We may be more aware these days of how we can get affected physically. But our mind will get affected by distorting our personality as well as our relationship with other people. The openness of our access with God and our sensitivity to the Spirit will also suffer. We may give place for feelings of guilt, doubt, fear and insecurity. Many times this kind of effect may not be observable immediately and we may not be aware of it, but nevertheless it will show in the long term.
God did not design us for sin but for a godly life. If we are godly, everything in us works well for us. But every time we sin it goes against us and distorts the image of God in us more.
The devil tries to deceive us by making us think that if no one knows what we have done we will not get affected by it. But it's with God that we have to do (He.4:13). Even though He forgives us graciously we cannot escape the consequences affecting us personally and those around us. We have more than enough trouble coming to us because we live in this world, but if we sin we are actually making more trouble for us ourselves!
God's plan of salvation is not merely to forgive our sins but also to make us into a people who can 'proclaim His excellencies' (1Pe.2:9). We proclaim this not just with our lips but also with God's fragrance that comes out of our daily life (2Co.2:14). The more we overcome the temptations that draw us to sin, the better this fragrance can be felt by people around us (2Co.4:10). We can overcome by the power of the Holy Spirit when we choose to deny the pleasures that temptations offer us and do the will of God in our life (Ro.8:13). Then it will conform us more into His image.