Adam Clarke on Psalms 100:4

Enter into his gates with thanksgiving - Publicly worship God; and when ye come to the house of prayer, be thankful that you have such a privilege; and when you enter his courts, praise him for the permission.

The word בתודה bethodah, which we render with thanksgiving, is properly with the confession-offering or sacrifice. See on Psa 100:1-5 (note).

Bless his name - Bless Jehovah, that he is your Elohim; see Psa 100:3. In our liturgic service we say, "Speak good of his name;" we cannot do otherwise; we have nothing but good to speak of our God.