This is a beautiful dua, Prophet Musa (AS) asked Allah to clear his chest, to make a mission of his easy, to let the knot of his tongue be loosened so that they can understand what he says. That is so the people could understand the message of Allah swt. What was the task?
Allah (swt) gave Prophet Musa (AS) a big task to go on a mission to see Firaawn (the pharaoh) and let him know that he has transgressed.
In Surah Taha, Allah teaches us a powerful lesson. When He takes something away from you, it is only to replace it with something even more amazing. All we need to do is keep our trust in Allah and His plan, and keep doing that which pleases Him.
In the Quran are stories to move your hearts, in it are duas to help you traverse this dunya in times of hardship and ease, in it are narrations to help you deal with the trials, no matter how difficult things seem.
RABBISH RAHLI SADRI FULL DUA IN ARABIC:
Here’s the full dua from Surah Ta ha in Arabic, it begins at ayat 25 and ends verse 28.