Its authority and ability to intervene has a lot to do with the idea that its word can be taken, and that it doesn't only favor the big powers. East Timor unlike other regions of Indonesia, which had been former Dutch territories was a Portuguese colony for centuries. After Indonesia invaded and annexed East Timor in 1975, the United Nations refused to recognize it. Only Australia recognized the takeover. After Kosova, the lie would be exposed if it didn't condemn Indonesia for its genocidal campaign in East Timor and not threaten stronger action.
International pressure is key to forcing the Indonesian army and ruling elite to leave East Timor.
It was international pressure along with the resistance of the East Timor people and May 1998 events in Indonesia that forced Indonesia to allow the U.N. referendum. The United Nation's credibility is at stake too since it assured the people who voted that they would be protected. While sending U.N. troops is not a long-term solution to East Timor's fight for freedom, it is a necessary first step to prevent a total depopulation of the territory by Indonesia. It must be done now, and not after the Indonesian assembly meets later in the year to ratify the vote. While suspending all economic aid by the IMF, World Bank and commercial contracts immediately is important, it is not enough to force Jakarta to stop the violence.