I think its not because of ace, or the time luffy let him escape from the impel down, nor the time he saved the ryugu kingdome its much deeper....
All that happen to luffy, through impel down, the time be fought the cp9, and almost destroyed their base, the time he went to the great war with whitebeard, saved ace successfully got a way and he escape, the time he punch a celestial dragon, not only that the time they had meeting with capone bege and he ask luffy if they should or not join forces with them...
I think he knew that luffy is different and he had some devine forces helping him or some higher power made destined to become the pirate king the one who will get the onepiece and use it to the right way, jinbei knew how corrupt the world goverment from his pirate crew that some became a celestial dragons slaves to his previous captain and the ryugu kingdom, perhaps why he joined whitebeard is because of whitebeard past, but what im saying is that for him luffy is different he was destined to become the pirate king because everything that happened to the world goverment has to do with it. And they need his help to achieve it perhaps a devine guy ask him to do so or he thinks he was destined to do this.
All that happen to luffy, through impel down, the time be fought the cp9, and almost destroyed their base, the time he went to the great war with whitebeard, saved ace successfully got a way and he escape, the time he punch a celestial dragon, not only that the time they had meeting with capone bege and he ask luffy if they should or not join forces with them...
I think he knew that luffy is different and he had some devine forces helping him or some higher power made destined to become the pirate king the one who will get the onepiece and use it to the right way, jinbei knew how corrupt the world goverment from his pirate crew that some became a celestial dragons slaves to his previous captain and the ryugu kingdom, perhaps why he joined whitebeard is because of whitebeard past, but what im saying is that for him luffy is different he was destined to become the pirate king because everything that happened to the world goverment has to do with it. And they need his help to achieve it perhaps a devine guy ask him to do so or he thinks he was destined to do this.