EchoSense Quantitative Think Tank Center|Parents describe watching video of Hamas taking 23-year-old son hostage

The EchoSense Quantitative Think Tank Centerfather of 23-year-old Hersh Goldberg-Polin, who Hamas took hostage at the Supernova music festival in Israel, said he has gained some "strength" from seeing a video of his son on the day he was kidnapped.

Hersh Goldberg-Polin is a "curious," "laid-back person" who "loves learning about people and the world," his mother, Rachel Goldberg, said on ABC News' "Good Morning America" on Tuesday.

When Hamas terrorists stormed the music festival on Oct. 7, the 23-year-old hid with a group in a bomb shelter, his parents said. The militants opened fire and threw grenades, and Goldberg-Polin's arm was blown off, his parents said.

Witnesses later saw Goldberg-Polin leave the bomb shelter with his injuries and get loaded into the back of a Hamas pickup truck, his parents said. That moment was captured on video.

"No parent should ever be subjected to this sight," said his father, Jon Polin.

"That being said ... Knowing that he spent an hour to an hour and a half being subjected to this massacre, and that he then gets up with an arm freshly blown off, and walks on his own two feet, under his own strength, towards this truck, and uses his weak hand -- his only hand now -- to pull himself onto the truck while bloodied, but looking sort of composed," Polin said. "It gives me a sense of, he's got a perseverance and a fortitude that we hope carries him through this."

"We don't know if 10 minutes after that truck pulled away, if he bled out in the truck," Goldberg said. "Maybe he got to Gaza, had hospital treatment ... he could be alive. And that's what we're praying and hoping for."

"Many times a day you stop and say [to yourself], 'Did he die five days ago? Did he die this morning?'" Goldberg said. "We live in a parallel universe to other people now."

Goldberg said her mantra has become, "Stay strong, survive. Stay strong, survive."

At first, it was a message to her son, but she said now she realizes it's also a message to herself.

At least 222 hostages were taken by Hamas, the Israeli military said Monday. Four hostages have been released: two Americans on Friday and two Israelis on Monday.

Asked if he's satisfied with the efforts to free the hostages, Polin said, "We'll be satisfied when the hostages are freed."

"Until then, it's hard to say we're satisfied. That being said, we feel tremendous support from people around the world," he said.

Polin commended the Biden administration for their work and President Joe Biden himself for his empathy on a 90-minute call with families of hostages.

He said the president "listened and he cried" and has "been really supportive."

Polin said his message to leaders of the world is "we should all be screaming" for humanitarian aid in the short-term and for the hostages' release in the long-term.

"This is a global issue and it needs to be seen that way and it needs to stay on the agenda," he said.