Despite Adam and Eve’s sin God is gracious and allows them to live long and prosperous lives. The genealogy here is remarkable in how consistently people lived to old age. There is no mention of disease, violence or accidental death (however we know about Cain and Abel). I am curious about why people were only having children at age 100 but perhaps I’m missing something.
With the birth of Jesus God’s plan for salvation is implemented. We see all the parts of a thorough plan highlighted here: the prophecy of God’s intentions, the preparations, the herald (John) and the great commission if you like of Jesus at his baptism. The action is imminent. Adult Jesus has arrived. His ministry is beginning now. The call for response is both simple and profound: pay attention to this Jesus, the time for skin deep religion is over. Get serious or risk facing the axe of judgment. The baby in a manger is a sweet image that is nice to celebrate but the real action comes next.