The Arabic word "tafseer" linguistically means: an explanation, which is to reveal something that may be hidden or unknown.
In Islamic terminology, "tafseer" is the explanation of the meanings of the Noble Qur`aan.
Learning tafseer is mandatory based upon what Allah says in Surah Saad; 38:29, also from Surah Muhammad, 47:24
Contemplation over the ayaat and taking lessons from what they contain is what is required. This contemplation means to reflect over the words in order to arrive at their intended meanings.
The Salaf, would learn the Qur`aan, its words and its meanings:
from the hadith of Abu Abdur Rahman as-Sulamee ...:they narrated to us that when they used to learn ten verses from the Prophet (sallaAllahu alaihi wa sallaam), they would not go beyond them until they learned what they contained of knowledge and action..."
They would say, "We learned the Qur`aan, the knowledge, and the action thereof, all together."