Final answer:
The weaknesses of the Parallel Model are the challenge it poses to human freedom, the lack of evidence for other minds, and the difficulty in connecting mind and body in idealism.
Step-by-step explanation:
The weaknesses associated with the Parallel Model, which attempts to integrate the principles of psychology and Christianity, include the challenge it poses to notions of human freedom and the lack of evidence for other minds. According to Leibniz's Psychophysical Parallelism, mind and body exist in a pre-established harmony, but this theory fails to provide a satisfactory explanation for how mind and body interact. Additionally, the lack of physical similarity in idealism makes it difficult to connect the two realms.