Bhashya
किं च यस्मात् ईशानात् अर्वाक्, यस्मादन्यविषय एवे-त्यर्थः, संवत्सरः कालात्मा सर्वस्य जनिमतः परिच्छेत्ता,यम् अपरिच्छिन्दन् अर्वागेव वर्तते, अहोभिः स्वावयवैः अ-होरात्रैरित्यर्थः ; तत् ज्योतिषां ज्योतिः आदित्यादिज्योतिषा-मप्यवभासकत्वात्, आयुरित्युपासते देवाः, अमृतं ज्योतिः-अतोऽन्यन्म्रियते, न हि ज्योतिः; सर्वस्य हि एतज्ज्योतिःआयुः ।आयुर्गुणेन यस्मात् देवाः तत् ज्योतिरुपासते,तस्मात् आयुष्मन्तस्ते ।तस्मात् आयुष्कामेन आयुर्गुणेनउपास्यं ब्रह्मेत्यर्थः ॥
In plain words
And 'from which' means from the lord himself; 'short of' means it never gets past him — that is the sense. The year, time itself in embodied form, marks the limit of everything that is born; unable to measure this lord, it stays forever short of him, moving only through its own parts, the days and nights. It is called the light of lights because it lights up even the sun and every other light there is. The gods worship it as life itself — the deathless light. Everything else dies; this light never does, because this very light is the life of everyone. And because the gods worship that light precisely as life, they themselves live long. So Brahman, carrying the quality of life, is exactly what someone who wants a long life should worship.
Close to the Sanskrit
Moreover, 'from which' means from the lord; 'this side of' means having a different reference — that is the meaning. The year, the embodiment of time, is the delimiter of everything that is born; failing to delimit which lord, it remains only on this side, 'by days,' that is, by its own parts, the day-and-nights — that is the meaning. 'That light of lights' — because it illumines even lights like the sun and so on. 'As life' — thus the gods worship it. 'The immortal light' — apart from this, everything else dies, but not this light; for this light indeed is the life of everyone. Since the gods worship that light because of its quality of being life, therefore they are long-lived. Therefore, Brahman, endowed with the quality of life, is to be worshipped by one who desires long life — that is the meaning.