How do we know that 'whosoever shall call upon the name of the Lord shall be saved' is true?

This statement appears in Romans 10:13, Acts 2:21, and Joel 2:32, establishing a biblical foundation that emphasizes its truth through repetition across different contexts. The declaration portrays God’s intention to offer salvation to all who call upon Him. Yet, this verse must be interpreted through the lens of God's sovereignty and grace; as seen in John 5:40 and Ephesians 2:8, the ability to call arises from God’s initiative. Thus, the assurance of salvation is rooted not only in the act of calling but also in the transformative work God performs in the hearts of those He saves.