Any sin, no matter how small will keep us from entering into heaven for "no unclean thing can enter HIS prescence." However, there are those sins that are easier than others to repent of. Some sins are more serious because full restitution is not possible. Murder- you cannot bring someone back from the dead. Adultry/Fornication- difficult to restore trust, may result in broken family, children born into suboptimal family environment. Other sins are more serious because they also reflect the "hardness of your heart" or distance of your soul from the "light of Christ." However, through the grace of Jesus Christ we can repent and forsake our sins and be justified and sactified through his holy sacrifice.