If we want to give special importance to one part of a sentence we can put it into a separate clause. There are two common ways of doing this. One is to use the structure:
It is/was…. that ….;
The other is to use:
What …. is/was …
Harry told the police. It was Harry that told the police.
I need a beer. What I need is a beer.
The sentence with It gives special importance to Harry; the sentence with What emphasizes a beer.
Let’s look at these structures in more detail.
The structure It is/was…. that … can emphasize any part of the sentence. Compare:
My mother threw an egg at the Minister of Education yesterday.
It was my mother who threw an egg at the Minister of Education yesterday.
It was an egg that my mother threw at the Minister of Education yesterday.
It was yesterday that my mother threw an egg at the Minister of Education.
It was the Minister of Education that my mother threw an egg at yesterday.
When the subject is emphasized, who is possible instead of that:
It was my mother who threw ….
The structure What …. is/was … is used to emphasize the subject or object. Compare:
My left leg hurts. What hurts is my left leg.
I like her style. What I like is her style.
“… and it was then that Dill gave us the idea of making Boo Radley come out”. (Harper Lee)
It was then that Calpurnia requested my presence in the kitchen. (Harper Lee)
It is with the greatest regret, therefore, that I must inform you that you do not fulfil our requirements. (J. Rowling)
It was this scar that made Harry so particularly unusual, even for a wizard. (J. Rowling)
“… but it was with a slightly softened expression that she started cutting Harry bread and buttering it for him”. (Rowling)
For a second he thought it was that, which had woken him. (J. Rowling)
It was with relief that they reached the oak front doors and eased them open. (J. Rowling)
It was a Tuesday that we had that talk. (Mark Twain)
What we want is to go out of here quiet and talk this show up, and sell the rest of the town! (Mark Twain)
So what we want to do is to be prepared; then we ‘re all right. (Mark Twain)
“What I want is my nigger; or what I want is my watermelon; or what I want is my Sunday-school book…” (Mark Twain)
“…I have as much soul and heart as you. It is my spirit that speaks to your spirit! We are equal in the sight of God!’ (Charlotte Bronte)
‘Naturally! Yes, but it is God we obey, not nature! (Charlotte Bronte)
What this lawyer says is true. I’ve been married, and my wife still lives! (Charlotte Bronte)
What I really should do is change my character, and I still could but – it’s difficult. And if I can’t have happiness, I want pleasure, even if it’s wrong.’ (Charlotte Bronte)
It was then that I saw her wild, inhuman face! She removed the veil, tore it in two and threw it on the floor.’ (Charlotte Bronte)
The wind, I thought, was shaking the door, but no, it was St John, who came in out of the frozen darkness, his coat covered in snow. (Charlotte Bronte)
Naturally, when I made this suggestion to St John and his sisters, they protested strongly, and it was with great difficulty that I finally managed to convince them of my firm intention to carry out this plan. (Charlotte Bronte)
‘Well, ma’am,’ the hotel-owner told me, ‘I was one of Mr. Rochester’s servants at the time, and I can tell you it was his mad wife who started the fire in the governess’s room. (Charlotte Bronte)