God says in Isaiah 44 verse 6:
6 “Thus says the Lord, the King of Israel,
And his Redeemer, the Lord of hosts:
‘I am the First and I am the Last;
Besides Me there is no God.
In this verse God insists He is the only God, the only object ultimately worthy of our attention, focus, praise and worship. Humanistic thinking might object to that, complaining that that is egocentric and self promoting of God to insist He gets all the attention and glory.
The truth is the opposite. God insists He is the only object worthy of our worship and worthy to build our lives around because He knows if we build it around anything else, if our life orbits around any other axis, it will hurt us and lead to a life that is less than it could be.
God wants to avoid confusion for our sake, so He insists that He exists in our minds on a “blank” piece of paper, uncluttered by any competition or rivalry. He knows He is what we need, He is the remedy, medicine for our ill state. He wants to save us wasting our time and life on false and counterfeit remedies and solutions, therefore telling us He is the only God.
God’s insistence on having no rivals is an act of love and mercy towards us. He wants us to get what we need, Him, with no delay, detours or distractions.
God declares Himself the one and only God, to save us pain.