I can agree that God was speaking to ancient Israel because that was the only nation that God was dealing with.
However, in the Bigger Picture Isaiah 1:18-19 can apply to everyone in now setting matters straight with God.
It would be now possible to reason together and to change because Isaiah 2:2-4 includes our time of our last days of badness on Earth as described at 2 Timothy 3:1-5,13; Romans 1:16, 29-32.
'Being willing and obedient' (Isaiah 1:19) would now include Jesus' instruction of Matthew 24:14 to tell others about the good news of God's kingdom of Daniel 2:44, and later 'eat the good of the land' as brought out at Micah 4:3-4 because as Jesus promised that the humble meek people will inherit the Earth.
Well first you would to explain how exactly
Isaiah 1:18,19 can apply to everyone.
When it applys to the Sacrifices that Israel was doing,
Unless you believe those sacrifices are still being done by Everyone to day.
That of 2 Timothy 3:1-5,13, and
Romans 1:16, 29-32, is all about the end times.
Do you understand what Jesus was referring to in Matthew 24:14. Have you any idea or clue when this all takes place and by who ?
Have you any idea or clue what Jesus is taking about in Matthew 24:19--"Woe unto them that are with child, and to them that give suck in those days"
Have you any idea or clue when this all takes place and it means them that are with child and what it means to them that give suck in those days.
You probably think it all means a woman with child, and giving the child breast feeding. Are you absolutely positively sure about this ?