Raising taxes and slashing welfare spending

"Greece's last bailout expired on Tuesday and Greece missed a €1.6bn payment to the IMF.
The European Commission - one of the 'troika' of creditors along with the IMF and the ECB - wanted Athens to raise taxes and slash welfare spending to meet its debt obligations.
Greece's Syriza-led left-wing government, which was elected in January on an anti-austerity platform, said creditors had tried to use fear to put pressure on Greeks."
http://www.bbc.co.uk/news/world-europe-33413569

I wonder how raising taxes and slashing welfare spending could contribute to the recovery of the economy. In addition to this, does Greece have a lot of rich people who evade taxes? Is welfare spending in Greece too much compared with the other EU countries?