In cleft sentences the information which could be given in just one clause is divided into two parts for contrastive or emphatic purposes. So, the sentence:
is rephrased as
In this way the first part of the sentence is brought into focus. There is an implicit contrast between my father and someone else. The new information is provided in this first part, always following the verb be, and the second part is treated as old information and becomes the tail. Then the nucleus of the IP is placed on the last lexical item of the first part. It is interesting to note how grammar and prosody are combined here. As Downing puts it, “the devices of intonational prominence and syntactic structure reinforce each other”.