Under the tutelage and leadership of Muhammad Ali Jinnah, the Muslim League set about increasing its membership and getting its message across. They started many more branches and invited more influential people such as the chief minister of Punjab to join them. This increased their party's reach and support.
More Muslims realized the need for representation especially after riots and religious restrictions showed the Muslims that the Indian National Congress was very much a Hindu party.
After the 1937 elections, the League did some introspection and tried to fix areas they felt they were lacking after seeing how they performed. They therefore gained experience from the 1937 elections that they used to build themselves into a more efficient party.
Answer: In that excerpt he means that he has an advantage because he swore and oath to defend the government when the south did not have one to destroy it.
