Isaiah calls us to repent and recognize God as the One and Only. In this case, repentance means no longer fearing, loving, or trusting in anything more than Jesus. Only the One True God can save! Only the One True God is worthy of worship!
This is a WELS sermon on the readings from Year C Lent 6 (Palm Sunday): Blessed is he who comes in the name of the Lord! He is our everlasting King and also the sacrificial Lamb of God. Readings are Isaiah 45:22-25; Psalm 24; Hebrews 12:1-3; and Luke 19:28-40.
Check out this video for more on the 1st Commandment: https://www.youtube.com/watch?v=P_7fbvsmrdU&list=PLMCGiH-la-918EaPNi_VK7AbgJRwKx5j8&index=2