The placement of Mercury in Virgo indicates you have a need for perfection at the mental level. Much of the behavior and many of the personality characteristics associated with Mercury in Virgo are a result of this need to be mentally occupied with constant examination and improvement. Mercury is well placed in Virgo, since Mercury rules Virgo. Thus, those functions associated with Mercury have a particularly strong affinity for the Virgoan energy and the attunement of those functions to the Virgo vibration strengthens and empowers them. 

Virgo is the Mutable Earth sign and the changeable earth nature of Virgo symbolically forces Mercury’s changeable airy nature to take on form and structure.  This allows those functions to be applied to concrete situations, bringing the mental quality associated with Mercury down to earth. The ability to apply the Mercury-associated functions concretely and practically makes them extremely relevant and, thus, tends to bring them to the forefront of your personality. 

Insecurities

With Mercury in Virgo, if you are insecure in yourself, then you will have an inherent lack of trust in what cannot be verified with logic or the senses. Your ego cannot face the reality that there are things that cannot be known by the mind. In fact, once logic and the senses are abandoned, the ego itself is shown to be an illusion. Logical empiricism, therefore, becomes a self-preservation defense of the ego. For you, having Mercury in Virgo, only that is real which you can perceive with your senses or verify with your logic. Such a stand, whether conscious or unconsciously held to, ultimately compels your mind to analyze everything down to the smallest iota in its quest to verify “reality.” You never make a leap of faith and, because you are obsessed with examination and analysis, your “action” is all mental. 

Mercury in the 6th House:

As the natural ruler of the 6th House, Mercury is well placed. It is the intellect, with its discriminating faculty, that is the psyche's chief tool to accomplish the 6th House objective of self-refinement. Also, in the derivative spheres of  6th House activities - work, health and service - it is the intellect and the communication function that are most useful and usually provide you with the greatest  level of satisfaction. Thus, the functions symbolized by Mercury are those that are naturally brought to the fore in those activities that are associated with the 6th House. Typically, the mental and communication functions will be strengthened by their use in these 6th House activities. 

Mercury’s placement in the 6th House symbolizes your tendency to apply your intellect to useful service. You are likely to gain a great deal of satisfaction from mental work and communication. A potential danger of having Mercury in the 6th House is that the mental and communication functions become limited through your absorption in the activities associated with the 6th House. These activities tend to practical and you may be disinclined to turn your mental energy to pursuits that do not have obvious utilitarian benefits. 

For the individual with Mercury in the 6th House, the realm of self-improvement offers an avenue through which you can expand your mental realm. It may be true that you confine yourself only to those forms of self-improvement that show tangible benefit, but you also have opportunities for self-development on more subtle or transcendent levels. Here, the analytical faculties symbolized by Mercury are engaged more abstractly, but with a purpose of refining your personality and the self.