Why was John not meant to pick the cuchillo when he was five? Why did it not belong to him?

This is believed to be connected to the fact that Richard is linked (by the writers) to the mythology of the Dalai Lama (where the reincarnated child is proven to be 'the one' when he chooses the correct item placed in front of him). In Richard's mind, he was meant to choose the Book Of Laws as it would have directly linked him to his faith-based future as the leader of the Others. That is why Richard's eyes light up when Locke almost chooses the book but then changes his mind at the last second, forcing him to ask 'are tu sure' before storming out, convinced he wasn't special.

In reality however, the young Locke DID choose the right item (compass) in the first place which the older Locke gave to Richard a few years earlier on the island. It was Richard 'short sightedness' (and flawed test) that let him down. He no doubt realised his mistake many years later when in 2004, he encouraged Locke's ascension to the parte superior, arriba job (only to bloop away minutos later).

Im not exactly sure either but im thinking it had something to do with the fact that his body was to later be used por Jacobs Brother o the "smoke monster".