Zos Chanukah

זאת חנוכה means the kedushah is so great on this day that tzaddikim are literally able to see it.

"But this revelation is only for the perfect tzaddikim. It states (Tehillim 118:23), היתה 'ה מאת זאת, we believe that Hashem gives this revelation on חנוכה זאת; however, נפלאת היא בעינינו, we can’t see it... Although we don’t see or feel this special revelation, we are happy for the tzaddikim, for we believe that they see it, and we rejoice in their joy."

בי חפצת כי ידעתי בזאת (Tehillim 41:12). The Yismach Yisrael explains בזאת, since you gave us זאת חנוכה, I know that You desire me and that You want to grant me goodness and chasadim.