How would you know about the sacrifice?
How would you know a sacrifice was required?
How would we know the sacrifice was accepted?
Word of mouth from other believers
John 20:18 Mary Magdalene came and told the disciples that she had seen the Lord, and that He had spoken these things to her. [see also Matt 28:8]
Preachers
Acts 2:14 But Peter, standing up with the eleven, raised his voice and said to them, “Men of Judea and all who dwell in Jerusalem, let this be known to you, and heed my words.
Many other instances in the book of Acts.
Romans 10:14 How then shall they call on Him in whom they have not believed? And how shall they believe in Him of whom they have not heard? And how shall they hear without a preacher? 15 And how shall they preach unless they are sent?