I am so confused

I want to understand something that my top does to me. Usually we rarely talk because we don’t like to talk while being physical. So when he is doing his initial entry he gives me these surprise thrusts when I am trying to open up myself wide. I don’t understand the point of doing this because no way he is going to entry in me this way because as soon as he does this I have to clench myself. Then again he starts slow and gives me a very powerful surprise thrust again. Why does he even do this? I have usually observed that he does this when we do it after a little while.