Bitcoin Mining is an extremely complex process where mining pools, that is, machines, do the solving of extremely complex mathematical calculations and when they solve these problems, they are rewarded with satoshis (fractions) of bitcoin! In simpler words, it is mining that causes new bitcoins to enter the market.
The fastest machine in solving these mathematical problems will be rewarded the most, while the not so fast machines, although they are also rewarded, their rewards are much smaller.
That's why they say it's impossible to hack btc, because to invade this network so strong, even the strongest in the world, it is necessary to have a machine even stronger than that of the miners: an impossible task.
"Oh, but there's quantum computing that's coming." Yes, Google itself is in the process of "development" of a quantum supercomputer capable of breaking cryptography, however, it is still a long way from having a power capable of destroying the Blockchain. Not to mention that as technology in general evolves, the crypto world evolves double, so there is nothing to worry about.
It is Bitcoin Mining that makes your Blockchain so secure.