Unity' refers to the 'sameness or reference between constituent parts of a unit'. The very concept of a unit necessarily rules out the possibility of speaking of totally diverse things within the unit. Appropriateness of reference within a unit is not enough. Grammatically this sentence is perfectly correct, however, semantically it is all askew. The reason is of course that the concepts used are inappropriate to their use in the sentence.
Coherence also has to do with relationships between statements.
As two separate statements they are perfectly proper. He put up his umbrella, that is, it started to rain. Thus it is apparent that two acceptable statements can be combined only with certain acceptable relations. 24 Prominence is the recognizing of one feature of the unit as more important than the other features. This feature is similar to the subject and complement idea statement in traditional exegesis.