The years of silence refer to the 429 years between the last book of the Old Testament and the birth of Christ. Malachi wrote the last book of the Old Testament around 433 BC. Christ was born in 4 BC according to Ussher’s chronology, used in the King James Bible ( and found on the Amazing Bible Timeline.)
Genesis 4: 3-5 states that Abel brought the firstlings of his flock of sheep as an offering while Cain brought fruits and vegetables. God respected Abel’s offering but not Cain’s. Why? Did God just like Abel better?
This offering and the offerings of later prophets even before Moses tells us that from the beginning men were taught of the coming Messiah, the sacrificial lamb and the need for a blood atonement. Abel responded and brought the required offering. Cain could have arranged to get such an offering through trade or other means. Instead, he brought his own idea of an offering and completely missed the point.
However, God did not let Cain go without a chance for redemption. He told Cain that if he did well, his offering would be accepted. And if not, then sin was at the door.