Do all things without grumbling or disputing, (ESV)
Anyone who has children will likely identify with the words Paul has written in this verse. As parents we tell our children to do something and it can be a rare occurrence when our child responds without grumbling or disputing! I can remember what would happen if I grumbled or disputed something my father said. If I did not like what he had just asked me to do, it was about to get worse. My grumbling would guarantee me even more tasks that I was not interested in.
So, what's the big deal with grumbling or disputing anyway? Well, let's look at both words individually and figure it out. Grumbling is literally a low, muttering word of unhappiness at what we have been asked to do. It belies an attitude of the heart that is selfish, and not the attitude of a faithful servant.
How about disputing? Disputing is a more direct negative criticism. Understand here that this disputing is in the context of receiving Godly instruction of what to do. Someone who is disputing is essentially arguing with God and perhaps criticizing his way. This is rebellion. Both grumbling and disputing are wrong. One is quieter. The other is more aggressive. They are sinful.
In the previous verses of this chapter the Apostle Paul described the great humility of Jesus Christ. He was obedient to death. Even when it came to his physical body feeling the stress of knowing the crucifixion was imminent, he did not grumble or dispute. Look at his words in Luke 22:42 where Jesus struggles with what he is being asked to do:
 saying, “Father, if you are willing, remove this cup from me. Nevertheless, not my will, but yours, be done.” (ESV)
We are to have this same mind that was in Christ Jesus (Philippians 2:5). We can ask if he is willing to remove our task, but ultimately seek to do his will, not yours. No grumbling. No disputing.