When I was a little boy, my dad was building a fence around our backyard and as he remembers it I came running to him asking if I could help. My parents tell me that I had a kids version of the toolset with a toolbelt and a plastic hammer and things of that nature so I could imitate what dad did. However, on this particular day I wanted to use big boy tools. I want to do use my dad’s hammer. I asked him to use it and he, as any good father should, said absolutely no. But when he turned his back to me I picked it up anyways and proceeded to try and hit the fence with it as if I was hitting a nail. Turns out I missed the fence completely and slammed the hammer into my finger. Obviously this was a very traumatic experience for me as my finger swelled up and I cried really loud and my dad looked like a remiss father to my mother and so on and so forth. The point being, in the hands of my dad that hammer with useful. It had a purpose and he was capable and able to use that hammer to fulfill that purpose. In my hands, it led to disaster.
In Roman 6, Paul says, “Do not present your members to sin as instruments for unrighteousness, but present yourselves to God as those who have been brought from death to life, and your members to God as instruments for righteousness.” In the same way that my dad’s hammer was useful in his hand and harmful in mine, our lives fit the same concept. We really are simply instruments to be used for the purposes of righteousness or unrighteousness. When our lives are given over to sin and sin is allowed to run our thoughts and our minds and our actions we become instruments for unrighteousness harmful to the body of Christ. However, in the hands of a perfect loving Father, our lives are used for righteousness. As instruments of righteousness we are largely beneficial to the body of Christ and ultimately used for good. Paul notes this distinction in Romans 6.
There are two really remarkable challenges in this passage. 
First, the challenge to remember that we are simply instruments. By ourselves and in our own power we are useless. Our bodies and our talents and our time were made for a specific purpose in the same way that a trumpet was made to make music and a baseball bat was made to hit homeruns and a hammer was made for construction. That purpose however is only achieved in the hands of someone skilled enough to use it. In the hands of a loving, perfect, holy God we are instruments used for righteousness. Regardless of our specific purpose that purpose is one centered on the righteous exultation of God’s glory. This presents a challenge to the believer. What is your greatest desire? Where do you place your greatest hope? What gets you most excited and what gets you most motivated? Is it the glory of God or is it your own exultation? Instruments used for righteousness are those who make much of the Creator God who holds that instrument in His hand. 
Secondly, are you willing to trust in the God that holds you? We like to believe we are capable and we are powerful and we, in and of ourselves, are solely responsible for the outcome of our lives. We see this in music and media all the time. The “I am the master of my fate” idea tricks us into believing that not only are we the instruments of righteousness but also that we are solely responsible for the usage of that instrument. We literally believe ourselves to be not only the sword but also the soldier. However, Romans 6 makes it clear, we are the sword and God is the soldier. Are we willing to trust that He knows how best to use us? Are we willing to give over our own plans and how we believe things should work to allow God to do with us as he sees fit? The challenge that comes with being an instrument of righteousness is that only God is righteous. Therefore to be an instrument used for righteous gain we must be in His hand and trust His purposes. Any other way leads to sin.
I was a little ahead of myself as a kid to think that I was equipped enough or mature enough to use my dad’s hammer. My mom and my dad both knew that to be true but I believed I knew best. We often do this with the Lord. Our lives are best used for His glory and for purposes of righteousness when we are in His hand. Trust him with it.