The purpose of a brute force attack would be to find a private key that would generate the same Public Key as used by your wallet. We call this a 'collision attack'.
The key we create has a length of 256-bit, which equates to 128-bit entropy. This key length has been accepted by the de facto standard in the crypto community. We can cite the bitcoin wiki: "it is more likely that the Earth is destroyed in the next 5 seconds, than that a collision occurs in the next millennium."