This belief gave immense power to the priests and the Pope, who was the highest titled priest of the world. The priests used that power of intercession to ensure the growth and prosperity of the 'church' to the detriment, many times, of the citizenry that made that immense power and wealth possible. Many times, the arrogance and power that were wielded by these priests caused an environment of resentment among the people that were supposedly being served.
Not only was this power a continuing slap in the community's face, but salvation was also for sale! In order to raise funds for more and more elegant buildings and to support the avaricious appetites of the clergy individuals were told that the only way to be "saved" was by literally paying for your sins. An individual at that time may have to do a few "hail Mary's" but in order to ensure salvation, silver and gold coins given into the hands of the local monasteries was by far and away a more viable option.
This air of resentment and anger had been simmering for decades and along with the 'salvation for sale environment" was part of the problem according to Luther's eyes.