"It's not just about money," Martial said. "It's to play and to enjoy it. That's it. That's why I chose to come here, to play and to enjoy football again."
Martial, 26, made only 11 appearances in all competitions for United this season.
"I want to play more and show what I can do," he said. "I believe Sevilla is the perfect place to do that. I want to score goals, provide assists and be crucial for this team in the next five months. There are many good players at Sevilla and I want to bring my experience to the side."
Sevilla fought off competition from Juventus for Martial's signature.
"It [negotiation] hasn't been easy," Martial said. "But from the first day, I knew I wanted to come to Sevilla and we all worked for that to happen.
"The coach [Julen Lopetegui] and the sporting director [Monchi] showed a strong interest in me and that's what convinced me to come here.
"They [Sevilla] wanted me in the past and we kept in touch. They contacted me recently and said I could help them."
Sevilla are second in LaLiga and are in contention for their seventh Europa League crown.
"I want to help the club achieve it's aims," he said. "We have to be consistent in LaLiga and do the best we can knowing that there are other big clubs that want to win the title."
"I have trained a lot in the past few months. I want to adapt as soon as possible to the team and connect well with my teammates to help them reach the aims for the season. I'm ready to play."
Martial, who has a contract with United until June 2024 with an option for another year, is open to extending his stay in Seville beyond this summer.
"I have joined for five months but you never know what the future holds," the forward said.
"Karim is a great player, one of the best in the world," he said. "He could have won the Ballon d'Or this year. I'm happy to be playing in the same league as him."
Martial scored 79 goals in 269 games for United since his arrival in 2015 from Monaco. Sevilla are four points adrift of league leaders Real Madrid and resume LaLiga on Feb. 5 at Osasuna.