The Importance of Mass in Relativity

We have a certain amount of mass and a certain resistance to movement which is what we should call mass not how hard you are to push when you're going really fast. A proton moving at high speed doesn't have more stuff to it  doesn't have more gluons inside of it contributing to its mass It's the same proton just moving faster it has energy of motion which definitely will affect how you accelerate it and how you push it but it doesn't change what it is fundamentally.