It is a unique "spirit" in the entire animation.

The meaning of the Will of Fire: Young people are the hope of the future, and the older generation must trust and protect them. The sacrifices of the older generation are not meaningless, but will inspire young people to become the pillars of the future. (The burning flames of fallen leaves are a metaphor for the heroic sacrifice of the older generation, and the new leaves are a metaphor for young people)

For example, Naruto's will of fire is the way of ninja, moving forward bravely and doing what he says, this is Naruto Human tolerance. But there is a kind of ninja called Naruto, just like Sasuke's evaluation of Naruto: That guy is full of shortcomings and is almost useless. He relied on his own efforts to overcome it bit by bit and became the Hokage. What you should understand is not the current Naruto, but the Naruto who has grown up along the way.

Extended information:

The Will of Fire was created by Senju Hashirama. The successors of the Will of Fire include Tobirama Senju, Hiruzen Sarutobi, Kagami Uchiha, Tsunade Senju, Minato Namikaze, Kakashi Hatake, Shisui Uchiha, Itachi Uchiha, Naruto Uzumaki and other Konoha Ninjas.

Because when Senju Hashirama and Uchiha Madara established the Konoha Ninja Village, they hoped for world peace so that children would no longer be involved in cruel wars and grow up in peace. During Hashirama's teenage years, due to the brutal war, the average age of ninjas was only 30 years old. Hashirama's two younger brothers and Madara's four younger brothers died in the war. Both Hashirama and Madara hope for world peace so that children can grow up in peace and not die due to war. Therefore, the core of the entire anime is to inherit the will of fire, which is also the value of this anime.