Why did Gol D Roger give his straw hat to Shanks, and why did Shanks pass it on to Luffy? Is there any explanation for this in the manga?
Also, why do they love the hat so much? Is the cause for this love related to the passing of the hat?
Why did Gol D Roger give his straw hat to Shanks, and why did Shanks pass it on to Luffy? Is there any explanation for this in the manga?
Also, why do they love the hat so much? Is the cause for this love related to the passing of the hat?
There was not much information on why the hat was passed down but I will do my best to give you an answer that I interpreted from the series.
Gol D. Roger to Shanks
Gol D. Roger wore the straw hat first and it seems the time period that he wore this hat was when he was gathering his crew together. It is not disclosed as to how long he held it from the time of his crew gathering to the new captains garb that he wore until his execution. It is probably safe to assume that once his crew was assembled he probably gave the hat to Shanks. It seems that Shanks wore this hat for almost all of his time on with the Roger Pirates and even a good deal afterwards even when he had his own crew the Red Hair Pirates. Exactly why Roger decided to give Shanks the hat is unknown at this point, but it would be safe to say that Roger saw something in Shanks and deemed him worthy of the hat. It can be said that many of the people that have the Will of the D. seem to be able to see the potential (whether for good or bad) in an individual.
Shanks to Monkey D. Luffy
After Shanks and his crew save Foosha Village from the mountain bandits and after Shanks loses his arm to a Sea King to save Luffy we see the Red Hair Pirates leaving the village. At this moment a young Monkey D. Luffy yells to Shanks that he will become a great pirate, even more so the Pirate King. After Luffy makes this statement Shanks gives him the straw hat and tells him to return it after he becomes a great pirate. The idea behind this gift is so that Luffy will put all of his effort to becoming a great pirate. Shanks wants Luffy to succeed and the hat is supposed to be both a challenge and encouragement from Shanks to Luffy. The challenge is to become as great of a pirate as he can be, ideally the King of Pirates. The encouragement is that Luffy will get to return the hat to his old friend once he becomes great. One characteristic that Luffy displays often through out this series is that he does not step down from a challenge no matter how hard or dangerous it may be.
The Love for the Hat
The love for the hat can stem from many sources. For Shanks it was the personal item of a man that he respected and most likely idolized. To receive a gift from a person with as much fame and reverence of that of Gol D. Roger is not something anyone in the One Piece universe would take lightly, it is in itself a treasure. During his fight with Buggy Luffy iterates that the hat is his treasure. To Luffy this hat being his "treasure" is the embodiment of his dreams of becoming the King of Pirates. He also loves the hat because of Shanks, it would be pretty easy to read that Shanks was one of Luffy's idols when he was young. Most children are very impressionable so it is along similar views with Gol D. Roger giving his hat to Shanks. Both Luffy and Shanks had a person that they viewed as an idol or person to surpass and the hat is can be represented as a dream, challenge, or promise. The thing is that the hat means something a little different to everyone so its hard to give the real reason as to why the hat is loved so much.
When crocus said to luffy when he had set sail to the grand line crocus "Is this the one who you are waiting for roger", maybe roger wanted someone to take his place to solve the mystery of Will of D - the one what roger cannot complete because of his incurable disease.
He gave the hat to shanks to give to someone who have D in his name.
This is just my theory