The vow of poverty seemed to be the lynchpin of templar banking, where the way to solve the basic principal/agent problem and ensure the alignment of interests to make the templars disinterested in the transactions themselves other than ensuring their integrity. Relating to money with a vow of poverty doesn't mean suffering, it's just a vow to eschew the trappings and symbols of wealth, as the whole system relied on Templars recognizing that they did not need money when instead they had power. They could afford to be humble. This problem of how to find and prove people who can be trusted to uphold higher values that create stability continues to today I'm sure.
If you are ever in Portugal, I recommend seeing the last Templar castle in Tomar. I found its scale and engineering quite spectacular, as well as how well it appears to have been preserved.