All of this relates to the specific kavanot that apply to each day of the 49 days of counting the Omer.
Generally speaking, at the seder of Pesach, on the first night, we receive a gift that is described in kabbalistic literature as our middot being properly connected and directed by our mochin.
When the Omer is brought, that connection is withdrawn and the middot are no longer directed by the mochin.
This connection is reestablished gradually through the mitzvah of counting the Omer.
Each day of the Omer is associated with a specific aspect of that reconnection, which is also associated with G-d’s Great Name (the one referred to in Kaddish) which is formed from the 42 first letters of the Ana B’Koach prayer together with the full portion of the name formed over that week. For detailed explanation of this name of G-d, see Pardes Rimonim by Rabbi Moshe Kordovero, Sha’ar 21 (פרטי השמות), chapters 12-14. And also Sefer Kehillat Yaacov, erech מ״ב and שמ מ״ב by Rabbi Yaacov Tzvi Yolles, the author of Melo Ro’im.
A second aspect of that reconnection is associated to the 49 words of the chapter of Tehillim said, beginning from after the introductory sentence and the 49 letters of the the middle sentence.
This is explained in detail in Sefer Kitzur Kavanot l’Ramchal in the section Inyan l’Sefirat HaOmer.