In plain words
Knowers of the three Vedas, purified of sin, drinking soma and worshipping Me through yajñas, seek the way to heaven. Reaching the world of Indra, the fruit of their merit, they enjoy in heaven the divine pleasures of the gods.
Word for word
The knowers of the three Vedas, drinkers of soma, purified of sin, having worshipped Me by yajñas, pray for the going to heaven; they, having reached the world of Indra, [the fruit of] merit, enjoy in heaven the divine pleasures of the gods.
The commentators
Bhagavadgītābhāṣyam
ये पुनः अज्ञाः कामकामाः —
त्रैविद्याः ऋग्यजुःसामविदः मां वस्वादिदेवरूपिणं सोमपाः सोमं पिबन्तीति सोमपाः, तेनैव सोमपानेन पूतपापाः शुद्धकिल्बिषाः, यज्ञैः अग्निष्टोमादिभिः इष्ट्वा पूजयित्वा स्वर्गतिं स्वर्गगमनं स्वरेव गतिः स्वर्गतिः ताम् , प्रार्थयन्ते । ते च पुण्यं पुण्यफलम् आसाद्य सम्प्राप्य सुरेन्द्रलोकं शतक्रतोः स्थानम् अश्नन्ति भुञ्जते दिव्यान् दिवि भवान् अप्राकृतान् देवभोगान् देवानां भोगान् ॥ २० ॥
In plain words
But those who don't know — the ones who want, and want, and want —
Those who know the three Vedas — the Ṛg, the Yajus, the Sāma — worship Me in the forms of the Vasus and the other gods. They're called soma-drinkers for the simple reason that they drink the soma; and by that very drinking, their sins are washed clean, their old faults purified. Through sacrifices like the Agniṣṭoma, having offered their worship, they pray for the road to heaven — heaven itself being the destination they're aiming at. And having earned that merit, having secured its fruit, they come to enjoy the very seat of Indra, lord of the gods — pleasures that are truly divine, born in heaven, unlike anything of this ordinary world, the very enjoyments that belong to the gods themselves.
Close to the Sanskrit
But those who, being ignorant, are desirers of desires —
The knowers of the three Vedas, [that is,] the knowers of the Ṛg, Yajus, and Sāma [Vedas], [worship] Me, having the forms of the gods beginning with the Vasus; soma-drinkers, [that is,] 'they drink soma' — thus [they are called] soma-drinkers; by that very drinking of soma, whose sins are purified, [that is,] whose transgressions are cleansed; by sacrifices beginning with the Agniṣṭoma, having sacrificed, [that is,] having worshipped, they pray for the way to heaven, [that is,] the going to heaven — [where] heaven itself is the goal, [namely] the heaven-going. And having attained, [that is,] having obtained, merit, [that is,] the fruit of merit, they enjoy, [that is,] partake of, the abode of Śatakratu [Indra], the world of the lord of the gods — divine, [that is,] arising in heaven, non-material enjoyments of the gods, [that is,] pleasures [belonging to the gods].