US aid worker Kayla Mueller left a gaping hole in her family's hearts when she passed away earlier this year, and her brother Eric is in deep pain after losing his "first friend, best friend, and only sister."

During a memorial service held at the historic Courthouse Square in Prescott, Arizona on Wednesday, her brother spoke to hundreds of mourners and encouraged them to continue his sister's legacy of kindness, the Gospel Herald shared.

"Let Kayla's heart live on through all of us and the people that she has touched in her life," he said. "Do what she would do. If you see somebody struggling, you see somebody upset, go give them a hug. Make the community even stronger. That's all it's going to do."

Kayls is the fourth American who was killed while held captive by the Islamic militant group. She went to Syria to help children affected by the civil war, but she was captured on August 2013 after she was leaving a Doctors Without Borders hospital in Aleppo. On February 6, the militant group sent a photo to her family claiming that Kayla was killed because of Jordanian air strikes.

Eric said in his speech that Kayla is in God's hands now, so at least she is free from harm and hurt. "You do not have to suffer anymore. Only now will you be able to see how much you really did and truly did for this world by looking down on it from above," he said.

Eric concluded that God works in mysterious ways, and said that sometimes, people just have to understand that He takes his angels home early, the same way He did with Kayla, who was only 26.

Kayla was a true angel of God, who inspired others to have strong faith and never lose hope even in the most dire situations. While she was being held captive, Kayla wrote her family an emotional letter, saying that "even in prison, one can be free" because of God.

"I remember mom always telling me that all in all in the end the only one you really have is God. I have come to a place in experience where, in every sense of the word, I have surrendered myself to our creator b/c literally there was no else....+ by God + by your prayers I have felt tenderly cradled in freefall," she wrote.