For the one who desires wealth and is incapable of realizing the Lord (neśvaram jñātuṁ śaktaḥ), due to the absence of adhikāra (eligibility) for tyāga (renunciation), the śruti prescribes duty-bound karma:
Here (iha), in this domain of karma-adhikāra—that is, the earthly realm (bhūloka)—one should perform (kurvan) the obligatory karmāṇi such as the daily agnihotra, etc.

The term eva (certainly) excludes desire for fruits (phalābhisandhi).
One should wish to live (jijīviṣet) a hundred years (śataṁ samāḥ).
In this manner (evaṁ), through the performance of the said karma, for you (tvayi), the one who considers oneself a doer (nara-abhimānin), karma—specifically aśubha-karma (inauspicious action)—does not bind (na lipyate).

From this (itaḥ), namely, the performance of svavarṇa-āśrama-appropriate karma, anyathā (other than this), there is no alternative means (sādhanāntaraṁ) by which the taint of aśubha-karma may be avoided.
This is the import: there is no other way to remain untainted by karma than this prescribed path.