 Because faith comes by hearing and hearing by the word of God, Romans 10, 17. And then they told him, you know, you must believe on the Lord Jesus Christ, you and all your household. We must believe that Jesus is the Christ, the Son of God. The gospel reveals that to us and evidence for why we should come to that conviction, that conclusion. But God so loved the world that he gave his only begotten Son that whoever believes in him should not perish but have everlasting life, John 3, 16. We must repent of our sins because God has commanded all men everywhere to repent. There's a day of judgment coming, Acts 17, 30 and 31.