This is only one of the first 3 verses in which the Psalmist calls on the people to publicly acknowledge God for His wonderful characteristics of being good, faithful, and merciful. This faithfulness is the word which is used so many times in the Old Testament of the kind of love that only God can show to people who deserve nothing (which is all of us). It is a love that lasts forever because God is eternal. Have you trusted in this Jesus for your salvation understanding it is He alone who gives this kind of love?
Psalm 136:1 Give thanks to the LORD, for He is good, for His faithfulness is everlasting.