When we approach an aspect, we need to access the basic language of astrology in order to find our answer. In the above case, we need to define Mars, define Neptune, define the nature of the natal chart, define the nature of synastry and define the nature of the square. When we have put these altogether, we will have our answer.
Mars—Mars is the go getter part of the human being. Mars is one’s drive. One may be assertive. One may be passive. Mars and it’s aspects in the natal chart will show us which. Let me give a simple example. If a Mars in Cancer wants to ask a girl for a date, he may ask his friend to ask her because Mars in Cancer is uncomfortable with his drives. If a Mars in Scorpio or Aries wants to ask a girl for a date, they will walk up to her and ask. A Mars in Libra will take so long to decide that the moment will have passed. I hope you get a sense of Mars.
Neptune–Neptune is one’s creativity. It is, also, an area in which one may not see life clearly i.e be deceived. Neptune is the planet of the next dimension. All creativity and imagination accesses the next dimension. All addictions access the next dimension because they are an ESCAPE from this dimension.Neptune is the planet that allows us to escape/leave the material world.The manner in which we do so can be indicated by the natal chart. For example, a person with Neptune in exact conjunction with the Sun may be an addict. This is a classic aspect for addiction. On the other hand, Neptune trine Mercury is the classic aspect for a writer. Neptune trine Mercury escapes the material world through the vehicle of imagination.
Square–The square is an obstacle. The square is a thwart. A square will present a kind of wide brick wall. One cannot climb over it. One cannot tunnel under it. One must use other positive aspects in the chart to meet his ends. The square will remain what it is, in my opinion. It is immovable.
The Natal Chart–The natal chart is the BLUEPRINT of the nature of each person. Think of a blueprint of a house. It displays the plumbing system, the electrical system, the design of the house etc.
The Synastry Chart–The synastry chart uses the natal charts of two people and compares them. We can see the BLUEPRINT of the relationship.
Now, onto the subject.
Mars square Neptune in the natal may make it hard for the person to set goals and meet them. The reason may be that the person has a great desire to escape the material world. Also,the native may not be able to access his creativity and use it in a PRODUCTIVE way. For example, he may be an amazing musician but may not have the practical attributes to hire the right manager and do the other practical things that are the backbone of any business, even a creative enterprise.
In the synastry, the Mars person may try to motivate the Neptune person. The Neptune person may try to escape. The Mars person may tell the Neptune to hire a manager, as in the other example. The Neptune person may get angry and resent the Mars person.
I hope that answers the question for Linda, the lovely lady who asked. Sorry for the delay.