Here St. Dominic is beating himself with a chain and calling it a posture of penance. Believe it or not, there are still some cultures which do this kind of thing around Holy Week. When a desperate teenager cuts herself we call it pathological or sick. Same difference.
The idea of God being somehow pleased or satisfied with his beloved children beating themselves with whips, chains or tree branches is pretty messed up. Jesus has taken care of the blood-letting by scourging and nail once and for all. Let's be done with it now.
But penance? As a kind of amends for sin? I get it - but I would suggest a penance that has some human value and meaning - that might build inner resilience and charity. Here it comes: Instead of beating yourself with a chain, quietly endure (put up with) other people. O my! For many of us this might be a much more difficult penance than drawing blood with sticks.
As a penance, put up with people who are slowing down.
As a penance, put up with the folks who need you to explain two or three times.
As a penance, put up with the folks who seem to be marginal.
As a penance, put up with the waiter who's not up to speed.
As a penance, don't lament the humidity, rain, ice, heat or cold. How tiresome!
As a penance, don't complain about the lousy sermon.
As a penance, don't whine about the food that's not right.
As a penance, don't groan about the walk that's too far.
As a penance, don't gripe about the cost of everything under the sun.
As a penance, endure the stranger who's hygiene is lacking.
As a penance, endure the person who talks too much.
As a penance, endure the person who comes across as cheap.
As a penance, endure the person who strikes you as kind of unskilled, incapable
As a penance, endure the person who isn't funny (being funny is kind of a
requirement for acceptability these days, isn't it?)
Now this is real penance. Skip the whip. I imagine God rolls his eyes at all of that.
But remember this: people have to endure or put up with ME - in all my superficiality, pettiness, self-pity, limitation, ignorance, self-preoccupation. I may even have a sense of having to put up with myself.