The prophet (pbuh) described as the best day that the sun has risen upon is the day of Arafah. The day that you come to know your Lord, every single year.
All of us stood before Allah on that day, and it was upon us that an oath was taken, Alalh asked each and every single one of us, am I not your Lord? Allah asked each and every single one of us am I not your Lord? And all of us say, yes, we bear witness.
The day that represents one of the five pillars of Islam. The best thing that you can do that covenant over and over and over again.
The word Arafah means to come to know, to come to know who? To come to know your Lord, And if you know your Lord then you know yourself.
And if you know yourself then once you know your Lord and then you know yourself, then you will naturally know your own shortcomings in regards to your Lord, the blessings that He has bestowed upon you are prerequisite to understanding the deficiency with which you have responded, which then leads you to the most sincere version of your supplication, realize that the dua that we say throughout that day does not just have an acknowledgment of Allah’s oneness, but a praise for all of the blessings that He showers upon us throughout the year and the prophet (pbuh) taught us Sayyidul Istighfar.