This adventure is very much about identity. The Doctor is summoned to the aid of Winston Churchill as he fights the second world war, and immediately recognises Churchill's new war machines. They are in fact the Daleks!
However, their potency lies dorment. It is only through the Doctor that they realise their full potential (albeit a destructive potential in the case of the Daleks).
Later, Professor Bracewell discovers that he is part human, part robot. To make matters worse, the Daleks have programmed the robotic section of his body to act as an explosive device. To save the day, it is up to Bracewell to decide his identity. With the support of the Doctor and Amy he chooses life, and goes on to live it to the full.
Similarly, it was only through Jesus that Levi (a much-hated tax collector) became Matthew the disciple, and that Saul had his road-to-damascus experience and changed to Paul. In the words of Jesus "I have come such that everyone may have life, and have it in all its fullness".