Although Surat-ul-Ikhlas is one of the shortest surahs, it is very comprehensive in scope. The prophet even considered it to represent one third of the Qur'an which, according to many scholars, is because the surah summarizes one of the three major topics in the Qur'an, the other two being law and stories of earlier generations.
Surat-ul-Ikhlas deals with the absolute oneness of Allah. This is declared by the word "ahad" in the first ayah and explained by the three remaining ayat. It emphasizes the clear distinction between Allah (the creator) and everything else (His creation, including prophets, angels and heavenly bodies). He is one and unique and it's not befitting for Him to take any son, daughter or associates. The heavens and the earth and everything in between depend on Him while He is totally independent. Exalted, He is above every false claim they make against Him.
Realizing the importance of this surah, the prophet wanted us to internalize it. So much so, that he recommended we recite it up to 17 times throughout the day: 1 time after each of the 5 daily prayers, 3 times in the morning, 3 times at night, 3 times before going to sleep, and 1 time during the second raka'a of two sunnah prayers (the one before fajr and the one after maghrib).