Contradiction with Matthew 7:14
Isaiah 48:18 suggests peace like a river if only God's commandments are followed, while Matthew 7:14 states the path to life is narrow and difficult, suggesting a lack of peace.
Matthew 7:14: Because strait [is] the gate, and narrow [is] the way, which leadeth unto life, and few there be that find it. [Because: or, How]
Contradiction with Hebrews 12:6
Isaiah 48:18 speaks of peace and righteousness from following commandments, while Hebrews 12:6 suggests that God chastens those He loves, implying difficulty and correction despite obedience.
Hebrews 12:6: For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth.
Contradiction with Romans 3:20
Isaiah 48:18 implies blessings from following commandments, whereas Romans 3:20 indicates that no one will be justified by the law, suggesting that adherence does not lead to the peace mentioned.
Romans 3:20: Therefore by the deeds of the law there shall no flesh be justified in his sight: for by the law [is] the knowledge of sin.
Contradiction with Galatians 3:10
Isaiah 48:18 promises peace for keeping commandments, but Galatians 3:10 declares those who rely on the law are under a curse, contradicting the promise of peace.
Galatians 3:10: For as many as are of the works of the law are under the curse: for it is written, Cursed [is] every one that continueth not in all things which are written in the book of the law to do them.
Contradiction with Isaiah 57:21
Isaiah 48:18 promises peace for following God's ways, while Isaiah 57:21 states there is no peace for the wicked, implying that peace is not guaranteed simply by law-keeping.
Isaiah 57:21: [There is] no peace, saith my God, to the wicked.
Paradox #1
The contradiction or inconsistency in Isaiah 48:18 could be seen in the gap between the promise of peace and well-being for following God's commands and the reality of suffering and hardship experienced by many who strive to live righteously. Some might question why they do not see the promised peace despite their efforts to follow the teachings.