When Christians speak of the non-essentials of the faith it is within the confines and context of salvation. The saying that is often spoken of is that the doctrine "neither saves you, nor condemns you." However, when it comes to essential doctrines this has to do with salvation and being reconciled/justified before God.
While many doctrines may fall under the umbrella of non-essential (for salvation) it doesn't negate their importance in this life as being essential for daily living. One might use giving, as an example of sowing and reaping. It is an important topic, but it is not essential for salvation. However, it does play an important role in the quality of life, not only in terms of blessings but just joy in blessing others.
So while there are essential and non-essential doctrines, they all are important in actuality. Only some might be called a necessity, in so far as salvation is concerned.