What do we learn from "[Bo'u She'arav] b'Sodah"?
Rashi: It is with thanks [Radak - for His Chesed. Shocher Tov says that all Korbanos and Tefilos will be Batel in the future, except for Korban Todah and thanks. There will be no need to request needs of this world, for there will always be great good. People need only to thank Kel. There will not be sinners who will need to bring Korban Chatas or Asham.
Malbim: One who comes to a person, he comes in the gates with praises. After he gets his request, he leaves with thanks. One comes to Hashem with thanks, for He already gave to him His goods.
Why does it say "Chatzerosav bi'S'hilah"?
Malbim: In His Chatzer, you will fathom His Gevuros and praises, and you will come to praise Him.
Why does it say "Hodu Lo Barchu Shmo"?
Malbim: One cannot praise Hashem due to Himself, only due to goods that one received [from Him]. Via thanking for His benefits, one will bless His name; through this, he recognizes His praises.
