Summary: Psalm 100 encourages us to count God as our greatest blessing.
Psalm 100 (quickview)  begins with the heading, "A psalm. For giving thanks." As we read the Psalm we might wonder why nothing specific is mentioned for which we are to give thanks. The writer doesn’t say, "Give thanks for your food and clothes, your home and those you love." How can you say thanks without describing what you are thankful for. The Psalm shows us where our thanksgiving to God begins. It focuses on God not on what he gives.
The name of God, the LORD, stands out as we look at the Psalm Not only because is it in capital letters but also because it appears four times. Remember that the name LORD is God’s personal name. It means "I am." When God sent Moses to the Israelites he told him, "I AM WHO I AM. This is what you are to say to the Israelites: ‘I AM has sent me to you.’" (Exodus 3:13-14 (quickview) ) Some time later God gave Moses an explanation of what his name means. He said, "The LORD, the LORD, the compassionate and gracious God, slow to anger, abounding in love and faithfulness, maintaining love to thousands, and forgiving wickedness, rebellion and sin." (Exodus 34:6-7 (quickview) ) When you take the name of God, the LORD, and connect it to love and forgiveness and care you have something very special. It never runs out. When the "I am" God says something it doesn’t change. When the "I am" God makes a promise it will happen. Just the name of God leads us to give thanks.
Having the LORD as God would have been much different than having any other god for the people living when this Psalm was written. The gods of the pagan nations around Israel were vengeful and mean. All the peoples around them lived in fear and at times even hatred of their false gods. Some of the false gods were portrayed as uninterested and distant. What a difference it must have made to know the truth about God. That he is the LORD who cares about his creation and provides for it.
Once we identify the true God as the LORD we can begin to connect with the call to worship in this Psalm of thanksgiving, "Shout for joy to the LORD, all the earth. Worship the LORD with gladness; come before him with joyful songs." Our thoughts are directed beyond what God has done, or what he has given us to who he is. We give thanks to the LORD because he is God.
Then the focus becomes more direct, "Know that the LORD is God." When we use the word know we may have a number of meanings for it. To know may mean just to have a little knowledge about something. Or when we say we know something it may imply that we know it very well. In the original language this word means to know something very well. In connection with the LORD it means to know about him in our head but also to know and love him in our heart. The Psalm writer tells us knowing God means knowing him as the LORD.
Certainly the times have changed since this Psalm was written. The circumstances in the world have changed. The false gods that surrounded God’s people have changed. But new gods have taken there place. Now the gods of science, materialism, humanism, and all the other "isms" that surround us are just as uncertain as the pagan gods of ancient times. But the same LORD is God. Today this Psalm of thanksgiving calls us to shout, and worship, and know that the LORD is God. That is only place to begin the act of giving thanks.