After looking at what Jesus said is in the heart of man and that there is nothing good in it. What about my righteousness? Can't I live a righteous life that is pleases God and not do those things? Look at what Isaiah 64:6 says; "But we are all like an unclean thing, And all our righteousnesses are like filthy rags;". When I think of filthy rags I think of my grandfather's shop rags. He was a mechanic and the rags that he used working on cars were filthy, grimy and covered with black grease. I always feared getting that on me and still do to this day. It is so hard to get out of clothes or off your hands. Those rags could never be used for doing dishes or anything else for the oil had soaked into them and stained them. The only thing that they could be used for was working with the filth that came from under the hood of a car.
That is what our own righteousnesses is like. It is stained with the filth of our sins and nothing we can do can make it come clean no matter how hard we try. So where do we get the righteousness from to put on as our breastplate?
Paul explains this in Philippians 3:8-9, "But indeed I also count all things loss for the excellence of the knowledge of Christ Jesus my Lord, for whom I have suffered the loss of all things, and count them as rubbish, that I may gain Christ and be found in Him, not having my own righteousness, which is from the law, but that which is through faith in Christ, the righteousness which is from God by faith;"
The righteousness of Jesus is the righteousness that we put on. Through His blood can the stain of our sins be washed away. Like Paul said it is of no work of our own that we are made righteous, our works are still stained with sin. Our righteousness is found through faith in Christ. That is when we take on the mind set of Christ and our heart no longer follows after the things Jesus listed in Mark. We now seek the things of God. Yet we need His righteousness to protect us from the old self and what satan throws out there at us.