How do we know that the covenant of grace is eternal?

The covenant of grace is described in Isaiah 54 as an unchanging commitment of God to His people, indicated by phrases such as 'the mountains shall depart' but 'my kindness shall not depart from thee' (Isaiah 54:10). This solid assurance is reinforced throughout Scripture where God's faithfulness and the permanence of His covenant promises are emphasized. In Hebrews 13:20, we see that Christ is the mediator of an everlasting covenant, ensuring that the relationship between Him and His elect is secure through all eternity.