Why is it important to believe that Christ shall save His people?

Understanding that Christ shall save His people as stated in Matthew 1:21 is pivotal for the assurance of one's salvation. It emphasizes that salvation is not a mere possibility or attempt but a definitive action completed by Christ. The principle that 'He shall save' signifies the absolute efficacy of His atonement, removing any doubt about whether His sacrifice was sufficient. This belief encourages believers to rest in the finished work of Christ rather than rely on their efforts to complete what He has already accomplished.