Actually, the readings are very consistent with one another as they depict slightly different stages of the relationship between God and his people in which God offers salvation and gives the people an opportunity to choose it.
In the first reading, the king and the people are in mortal terror of being conquered, but the prophet Isaiah assures them of the Lord’s saving power, but he also says: “Unless your faith is firm, you shall not be firm!” In the very next verse after this reading, this faith would be mildly tested as the king is prompted to ask the Lord for a sign. The king would refuse God’s offer and the prophecy would turn dark for him, even as Isaiah would also prophesy God’s promise of salvation eventually bearing fruit in a far more wonderful way.
Listen, O house of David!
Is it not enough for you to weary men,
must you also weary my God?
Therefore the Lord himself will give you this sign:
the virgin shall be with child, and bear a son,
and shall name him Immanuel.
In the Gospel, Jesus has given unprecedented signs and proofs of God’s salvation, but many of the people have refused to accept it. Jesus is making it vividly clear that the alternative to accepting salvation is no salvation.
God offers us salvation, ultimate freedom from all evil and pain, and gives us the grace to choose to accept this salvation.
We have a choice. We have a chance. We need to remember this and to let others know as well.