US-P18.194ab तत्त्वमोस्तुल्यनीडार्थमसीत्येतत् पदं भवेत् ।US-P18.194cd तच्छब्दः प्रत्यगात्मार्थस्तच्छब्दार्थस्त्वमस्तथा ॥
In plain words
The word 'are' is there to put 'that' and 'you' in one nest — to say that both words come to rest on the same thing. 'That' refers to the Self within; and what 'that' refers to is exactly what 'you' refers to.
Close to the Sanskrit
For the purpose of the same-nest meaning of the two words 'tat' and 'tvam', this word 'asi' should be [understood to stand]. The word 'tat' has the inner Self as its referent; likewise the referent of the word 'tat' is [the referent] of 'tvam'.