Why does he thank Hashem with all his heart?
Radak: It was a great salvation for David and Yisrael when Galyus died.
Malbim: Thanks for the past will be with all my heart. Chovos ha'Levavos (Sha'ar ha'Avodah) says that the reason why it is hard for man to thank Hashem for His Chesed is because when he comes to thank for the past, his mouth thanks, but his intent is request. His heart intends to request that Hashem continue to do good to him in the future. If so, his thanks is not complete, for in his heart he thinks that what he received will not suffice, and he wants to add to it. I will thank You with all my heart, without intent to request.
What are "Kol Nifle'osecha"?
Rashi: They are the final redemption, which is equated to all the miracles - "people will not say, Chai Hashem who brought" [Yisrael up from Egypt. Rather, they will praise Him for the final redemption.]
Radak: For each wonder, a person tells also other wonders that passed - "Zecher Asah l'Nifle'osav" (111:4).
Malbim: This is unlike most people, who tell only open miracles, but things that appear to them to have natural causes, they attribute to nature and chance. My eyes are open to know that also natural ways are wonders of Hashem and hidden miracle. I will tell to inform that they are wonders of the One whose knowledge is complete.
