Mother Teresa is known for her work, caring for the poorest of the poor around the world, and Sunday, she will become known as Saint Teresa of Calcutta.
"You kind of felt like light and a breeze comes in and this just energy," Sean Callahan, chief operations officer for Catholic Relief Services, said about Mother Teresa when she walked into a room.
Callahan worked with her in Calcutta, where millions were without a home and dying in the street.
"When I was there, 3 million people lived on the streets, 1 million of them were children and the mission of charity would literally be pulling people off of the streets," Callahan said.
Working in the Center for the Dying, Callahan faced traumatic experiences.
"Once I was treating a man, I was feeding him and cleaning him and taking him to the bathroom and bringing him back and I went to go get something and I came back and he was dead. I then had to carry his body through the streets to the crematorium," Callahan said.
The next day, Mother Teresa greeted him and asked how he liked working in the center.
"I said it was okay, Mother, but you know someone died while I was there and that really bothered me. She said you are so lucky," Callahan said.
Mother Teresa explained he was lucky to have been with the poor man when he ascended to meet God.
Callahan said Mother Teresa found joy in everything in life.
"Peace begins with a smile, and so every person that you're near do you touch them with a smile, a little shake of your hand, is it the person who is walking down the street or in a subway, can you reach out to every single person?" Callahan said, adding he learned this from the blessed mother.
She spread this joy and love everywhere she went, including a trip to Baltimore in 1996.
"She jumped out of the car, that was driving her to CRS. I greeted her on the sidewalk and before I could get her through the CRS door, a young woman was walking by on her way home from work and Mother just reached out her hands and shook her hand. Could you imagine walking home from work and running into Mother Teresa?" Callahan said.
He said she was infectious, changing him personally to open his mind to ask, "What can I do for others?"
Callahan experienced this when he completed gruesome tasks in Calcutta, like holding a man down while a nun was deworming him. Sometimes he would have to throw a bucket of refuse out, and one day saw a woman dressed in rags emerge from the other side of the pile to rummage through it.
"That's when you know true poverty," he said.
Callahan was flown out on a medical helicopter, ill from bad water and the environment, but he came back to continue the humanitarian effort.
He later found and married his wife in Calcutta and now has two children.
He said he will never forget the sacrifices Mother Teresa made, and how she continued her work, even though she had doubts.
"Everyone is important and you can learn something from everyone in life, just listen and look around," Callahan said.
It's a lesson that can be learned today, and something that helped earn Mother Teresa the title of saint.