What kind of legal responsibility should I bear if I have reached the age of 14 but not reached the age of 16, providing a murder weapon and causing serious injuries?

It is also the crime of intentional injury, which belongs to one of the eight felonies. 14 years old can be sentenced or given a lighter punishment.

According to the circumstances, this accessory to the same crime can be exempted from criminal punishment.

Supplement:

For your question, it mainly depends on whether you know the purpose of his borrowing the knife.

In the case of intentional injury, the main basis for judging is whether there is intentional injury. If the knife is borrowed knowingly, there is intentional injury. Under normal circumstances, the person who moves the knife is identified as the principal offender and the actual accomplice who borrows the knife.