Having reached Me, the great souls do not take birth again, which is a place of sorrow and impermanent, because they have attained the supreme perfection.

mām upetya — having reached/approached Me. They do not reincarnate: na āpnuvanti punar janma — they do not obtain birth again.

Why: duḥkhālayam — abode of sorrow (all samsāra is thus), aśāśvatam — non-eternal, impermanent. The mahātmānaḥ (great souls) have attained paramāṃ saṃsiddhim — supreme perfection.