Surah Baqarah is named as such because of this story of the cow in it. It is a story that happened to the children of Israel in the time of Prophet Musa u, so as to affirm a very important principle from the important principles of faith which is, the resurrection.
And to have belief in the resurrection is the most important condition from the conditions of faith, second to the belief in Allah U. And it is the most important part of the parts of faith, that is, to believe in the last day and in resurrection after death. All people see death but they do not see the resurrection, hence it is unseen, and veiled, just like all the parts of faith such as the belief in Allah U, in His angels, in His books, in His prophets, in the Last Day, and in the Decree and Predestination, the good of it and the bad of it.