Put simply, the reason for these messages is to encourage you to act unreasonably! For to act in faith is an unreasonable thing, it means believing in God rather than circumstances around us. Abraham was able to sit & relax - perfectly reasonable - until God showed up and he sees three men.
Of course this is odd - one Lord appearing as 3 men, but for Abraham it is clearly significant since he springs into action and prepares a full blown feast. With the food being consumed the attention turns to Abraham's wife, Sarah. Mysteriously the narrative switches back to 'The Lord' (rather than the 3 men speaking) who declares that within a year she would have a baby. God's purposes are therefore actually through Abraham and Sarah as a couple, i.e. fulfilled through male and female.
This is important since cultures in the Bible were heavily paternalistic, and Jewish hereditary is typically all about the male line. Yet the Bible gives many clues that God honours the female and her role. A personal favourite are the accounts of 1 & 2 Kings/Chronicles, where king upon king is announced to be 'the son of X, and whose mother was Y'.
The birth announcement of course is huge, but the response is laughter - effectively a 'no way, that can't happen, I'm old ...'. Yet that is the point - faith is unreasonable! Reason says it can't happen, it is not possible ... but with God declaring it then it is possible. Will you live in barrenness, closed to a future that God can open, laughing off (i.e. resisting God) His purposes? Or can you live in the good news of what God says and promises, the God who can break even the hardest realities wide open?
The Lord asks 'Is anything too hard for the Lord?'. Again God uses a question, i.e. an invitation to the would-be parents, inviting them 'will you have faith?'. The question is about Sarah but is put to Abraham ... so all of us, men & women, ultimately need to answer for ourselves whether we will be embraced by God's promises or put them to the side. Hence the key question:
Key Qn: [UP] What is God saying to you?
Challenge: Don't laugh it off
Years later another woman will be given a birth announcement, this time
with no earthly father. Her son will be called Jesus, and thankfully her
answer was one of embracing faith. Can you embrace what God is saying to you, do you find yourself struggling with it, or do you even cast it off as if it was too hard for the Lord?