Can you please explain what Lincoln was doing in his speech, and what he wanted Congress to think?

Can you please explain what Lincoln was doing in his speech, and what he wanted Congress to think? "The dogmas of the quiet past are inadequate to the stormy present. As our case is new, so we must think anew and act anew. We must disenthrall ourselves, and then we shall save our country. Fellow citizens, we cannot escape history. The fiery trial through which we passed will light us down, in honor or dishonor, to the latest generation. We say we are for Union. The world will not forget that we say this. In giving freedom to the slave, we assure freedom to the free-- honorable alike and what we give and what we preserve, we shall nobly save more mainly lose the last best hope of earth".