“You have said in your heart”. Isaiah 14:13a
Our heart is very important as a vital organ of body as well as the seat of the seat of our thoughts and affections. It is the center of all our inner life. It is in this later sense God says, “You have said in your heart”.
What we say in our heart is significant. That's exactly what we do when we have a suitable condition. Because it is not known to others, many think they can think upon any thing and wait for an opportunity to execute it, and nobody will know about it.
Here the Lord rebukes Babylon for her pride. Many Bible students consider it as a reference to Lucifer the fallen angel who is commonly called Devil or Satan. It is he who energizes individuals as well as nations to rebel against God. Everything begins within the heart of man.
Mind is the battle field! Satan moves our mind to think and contemplate and that leads to an appropriate action at the right time. We read about how successfully devil instigated David to do something against God's plan. David paid heavily for it. 1 Chronicale 21:1ff. With Judas who betrayed the Lord Jesus Christ also Devil worked similarly, starting with a thought in his heart. John 13:1, 27.
No wonder Solomon the wise man, exhorts, “Guard your heart with all diligence”. Proverbs 4:23.
Be careful with our thoughts, affections and desires. Do not just deceive yourself. God carefully watches our heart, the innermost part of our being. Noting is hidden to the piercing eyes of the Lord.