Complex sentence: A portion of the A11 Bionic chip's neural engine protected within the Secure Enclave transforms this data into a mathematical representation and compares that representation to the enrolled facial data, which itself is a mathematical representation of your face captured across a variety of poses.
Split into simpler sentences: A portion of the A11 Bionic chip's neural engine, protected within the Secure Enclave, transforms this data into a mathematical representation. It compares it to the enrolled facial data, which itself is a mathematical representation of the user's face captured across a variety of poses.