Do you mean the "means by which you effect?"

Serving or Self-serving

in·stru·ment

[in-struh-muhnt]

–noun  

1.  a mechanical tool or implement, especially one used for delicate or precision work: surgical instruments.

2.  a contrivance or apparatus for producing musical sounds: a stringed instrument.

3.  a means by which something is effected or done; agency: an instrument of government.

We are all INSTRUMENTS.  There is a good and a bad, a black and a white, a wrong and a right; in everything we do.  Even the best of people can do things that affect those around them negatively, just as the worst can do deeds that have a positive affect on others.  

Even above both of these examples is the moral truth of good and evil.  

One way or another you are a tool of one of those, even if you think you are keeping to yourself and not bothering anyone.  Usually we get so caught up in the happenings of our lives that we become Instruments of SIN. (Romans 6:13- Do not offer any part of yourself to sin as an instrument of wickedness....)  

When we are dealing with our students, or those with whom we have friendships (or more), or those we work with...lets be MORE MINDFUL of how we affect those around us.