"echoing, restating, and clarifying what a client expresses is most central to the process of"

The correct answer is active listening.
If you are reiterating what the other person said, or paraphrasing their words, or asking them further questions, you will show them that you've been listening to them attentively and that you are interested in what they have to say. This is important if you want to let the speaker know that you actually understand what they are saying, instead of just passively listening.