God in His mercy has purposed and has intention for everyone to have a Story of Thanksgiving; while some already have their story.
…. and they overcame by the words of their testimony
The Testimony is their own Story of Thanksgiving.
Just as God has been merciful and faithful to us, so we also need to show our gratitude to Him. We need to continually thank Him because we can see Him and in His deeds.
If you take God for granted then you are grounded.
… bless the Lord O my soul and forget not His benefits
We need to be mindful that a full Thanksgiving Story is composed of