(CNN) -- A blockbuster movie could not have been scripted better: a woman whose unparalleled voice earned her the kind of single-name recognition that felt like an unbearable burden. Fitting, then, that superstar Kevin Costner should eulogize his co-star in this way. At Whitney Houston's funeral Saturday, Costner recalled a woman who doubted herself when she need not have. He revealed how Houston was chosen to star with him in the 1992 movie "the Bodyguard." Few had confidence in Houston -- she had never acted before. A lot was riding on this role, he said, and the studio was unsure about giving it to a black woman. But Costner thought she was perfect, though she would have to prove it to the studio with a screen test. In her trailer, he took her nervous hands in his; told her she looked beautiful. "I could still feel the doubt," he said. She asked for some time and after 20 minutes appeared for the screen test. "We hadn't said four lines when we had to stop," Costner recalled. "I needed to know what she had done in those 20 minutes." He stood her in front of a mirror, her makeup running down her face. In those 20 minutes, she had wiped off the studio makeup and applied her own, the thick heavy kind she wore for her music videos, the kind that melted under the heat of studio lights. She didn't think the lighter makeup made her look good enough. To Costner, Houston seemed so small and sad at that moment. "You weren't just pretty. You were as beautiful as a woman could be," Costner said in front of a packed Newark church. "Whitney, if you could hear me now, I would tell you: You weren't just good enough. You were great. You sang the whole damn song without a band." Costner, of course, was referring to Houston's signature song: "I Will Always Love You" from "The Bodyguard." "A lot of leading men could have played my part, but you, Whitney, I truly believe, you were the only one who could have played Rachel Marin." For her closest friends inside that church Saturday, and strangers who continue to draw inspiration from her voice, Costner's words hit a painfully honest note about human frailty. "It was the burden that made her great and the part that caused her to stumble again," he said. Years after "The Bodyguard" hit theaters, reports of Houston's struggles with drug addiction and a rocky marriage with Bobby Brown surfaced and her album sales declined. "The inexplicable burden that comes with fame," Costner said. "Call it doubt. Call it fear. I've had mine. I know the famous in the room have had theirs." Costner said Houston's own story could help a new generation of young girls who dream big. "Maybe they're thinking they aren't good enough," he said. "I think Whitney would tell you: Guard your bodies. Guard the precious miracle of your life. Then sing your hearts out, knowing that there's a lady in heaven who's making God himself wonder how he created something so perfect. "So off you go, Whitney. Off you go," Costner said in closing. "Escorted by an army of angels to your heavenly father. And when you sing before him, don't you worry. You'll be good enough."