How do we know the gospel is the only true message of salvation?

Acts 4:12 indicates that there is no other name under heaven by which we must be saved, affirming that Christ alone is the source of salvation. In the teaching of sovereign grace, the gospel declares that Jesus has fully satisfied the law and atoned for sins once for all. This singularity reveals that man can bring nothing of his own merit to God; instead, salvation is entirely dependent on the completed work of Christ. Thus, the assurance we have is not through human effort but through divine revelation in the person of Jesus, the true Savior.