to prove, like Jesus Christ, what people belonging to God would do for Him (God) for others. Prophets were sent to soothe, comfort, lead people to God (evangelise) and tell of God's truths.
Some delivered messages as oracles but not all prophesised the future. Although 'end time prophesies' are well understood now as we see fulfillment in hindsight and present times happening.
Prophets steered people in the right track, called people to repentance, healed by miracles (the work of God's power) but all called people to be saved - salvation. They did this by inter-acting with other people and teaching. Although they are all dead and gone from this world, their words live on and are being fulfilled just as God said they would be. Good news for some.