As an OVA, Major: Message's point is just to bring the entire series to a close. Gorou, who has faced many many struggles so far, but have always received support from his friends and family, becomes the one to support his family, with his only gift he can give to his kids, baseball. Throughout all seasons of Major, we've seen Gorou grow from a talented reckless kid, to a championship-winning professional in Major League Baseball in USA, while retaining his recklessness. But the biggest influence he's had is arguably from his dad. So now that Gorou has become the father, he sought to be the rolemodel to his kids, the way his father became his. And the only way he could do that after his injury, being the reckless that he is, is to show his kids, Izumi and Daigo, the result of his hard works; to show them that an obstacle is just another challenge to help them grow.
I know there won't be another season of Major, but if there ever is, this time it'll be the story of Izumi, the way that Major was the story about Gorou.