Why is it impossible to love God and neighbor perfectly?

The sinful nature of humanity creates a barrier to perfectly loving God and our neighbor. As stated in Romans 7:18, even when we desire to do good, evil lies within us, indicating the struggle between our intentions and actions. Jesus noted that the law is spiritual and requires perfect adherence, which we, in our flesh, cannot fulfill. This acknowledgment of our inability drives us to rely on Christ's perfect obedience and love, recognizing that we need Him to fulfill the law on our behalf.