Every single action we do, or situation we put ourselves in will affect our souls for the good or for the bad. 

In order to nurture us, God has set five categories in the Sharīʿa (or Islamic law) to guide our spiritual lives. 

1.  Wājib: Obligatory or necessary, like fasting.  
2. Mustahab: A recommended act. You don’t have to do it, but if you do it, you will get rewards.  
3. Mubāh: Neutral act, like drinking water regularly. 
4. Makrūh: Hated act, but if you do it, you won't be sinful. 
5. Haram: forbidden act. If you do it, you are sinning. 

Remember that all of these acts are subject to change depending on conditions. Something may be wājib like fasting, however, if it becomes dangerous for your health, then it becomes haram on you. The same thing does for a mustahab act. If a mustahab act impedes on your wājib acts, then the mustahab act becomes impermissible for you to do. 

Something may be harām for us, but under certain conditions it may become wājib. For example, if you’re stuck in a desert and you have nothing to eat and drink except for wine and pork and you see that you may die from hunger and thirst, then it becomes wājib on you to drink wine and eat pork!