Isaiah 54:10 NKJV
"For the mountains shall depart and the hills be removed, but my kindness shall not depart from you, nor shall my covenant of peace be removed," says the Lord who has mercy on you.
As God speaks affectionately to the children of Israel, He is emphatic about His covenant of peace with them. He said His covenant, which secured peace for them, would never be removed, even if the mountains and hills left their places. They knew that was very unlikely to happen, so it was a way of saying there is no need to worry about the covenant of peace ever going away. As Messianic Israelites, and people who have been grafted into the nation of Israel spiritually, and who have become heirs of the covenant through Christ, let us be comforted in knowing that we have a covenant of peace that will not go away.