शोधिते त्वम्पदार्थे हि तत्त्वमस्यादि चिन्तितम् ।सम्भवेन्नान्यथा तस्माच्छोधनं कृतमादितः ॥ २२ ॥
In plain words
Once the word "you" has been cleared of everything it is not, then contemplating "That you are" can actually happen. There is no other way in. That is why the clearing was done first, before anything else.
Close to the Sanskrit
When the meaning of the word "you" has been purified, then indeed the contemplation of "That you are" and the rest can come about; not otherwise. Therefore the purification was carried out at the very beginning.