BhG 14.18

syntax

sattva-sthāḥ (situated in sattva) ūrdhvam (upward) gacchanti (they go),
rājasāḥ (rajasic) madhye (in the middle) tiṣṭhanti (they stay),
jaghanya-guṇa-vṛtta-sthāḥ (those situated in the lowest guṇa) tāmasāḥ (tamasic) adhaḥ (downward) gacchanti (they go).

grammar

ūrdhvam	–	av. – upward (from: √vṛdh – to grow, ūrdhva – upper, high);
gacchanti	–	√gam (to go) Praes. P 1v.3 – they go;
sattva-sthāḥ	–	sattva-stha 1n.3 m.; ye sattve tiṣṭhanti te – those situated in sattva (from: √as – to be, PPr sant – being, existing, true, the essence, abst. sattva – being, essence, wisdom, spirit, one of the three guṇas; √sthā – to stand, stha – suffix: being in);
madhye	–	madhya 7n.1 n. – in the middle, inside;
tiṣṭhanti	–	√sthā (to stand) Praes. P 1v.3 – they stay;
rājasāḥ	–	rājasa 1n.3 m. – related to rajas, rajasic (from: √rañj – to be dyed, be excited, be delighted, rajas – coloured, dust, passion, one of the three guṇas);
jaghanya-guṇa-vṛtta-sthāḥ	–	jaghanya-guṇa-vṛtta-stha 1n.3 m.; ye jaghanyasya guṇasya vṛttau tiṣṭhanti te – those situated in the lowest guṇa (from: jaghana – buttocks, loins, jaghanya – lowest, worst, latest; √grah – to take, guṇa – quality, virtue, thread; √vṛt – to move, to happen, to act, PP vṛtta – set in motion; √sthā – to stand, stha – suffix: being in);
adhaḥ	–	av. – downward;
gacchanti	–	√gam (to go) Praes. P 1v.3 – they go;
tāmasāḥ	–	tāmasa 1n.3 m. – related to tamas, tamasic (from: √tam – to choke, to faint, to perish, to stop; tamas – darkness, gloom, dullness, passivity, one of the three guṇas);

textual variants

sattva-sthā → sattvena (by sattva);
jaghanya-guṇa-vṛtta-sthā → jaghanya-guṇa-vṛtti-sthā (those situated in the lowest guṇa);

Śāṃkara

kiṃ ca—
ūrdhvaṃ gacchanti devalokādiṣūtpadyante sattva-sthāḥ sattva-guṇa-vṛtta-sthāḥ | madhye tiṣṭhanti manuṣyeṣūtpadyante rājasāḥ | jaghanya-guṇa-vṛtta-sthā jaghanyaś cāsau guṇaś ca jaghanya-guṇas tamaḥ, tasya vṛttaṃ nidrālasyādi, tasmin sthitāḥ jaghanya-guṇa-vṛtta-sthāḥ mūḍhāḥ adho gacchanti paśv-ādiṣūtpadyante tāmasāḥ

Rāmānuja

evam uktena prakāreṇa sattvasthā ūrdhvaṃ gacchanti krameṇa saṃsārabandhān mokṣaṃ gacchanti / rajasaḥ svargādiphalalobhakaratvād rājasāḥ phalasādhanabhutaṃ karmānuṣṭhāya tatphalam anubhūya punar api janitvā tad eva karmānutiṣṭhantīti madhye tiṣṭhanti / punarāvṛttirūpatayā duḥkhaprāyam eva tat / tāmasās tu jaghanyaguṇavṛttisthā uttarottaranikṛṣṭatamoguṇavṛttiṣu sthitā adho gacchanti antyatvam, tatas tiryaktvam, tataḥ krimikīṭādijanma, sthāvaratvam, tato ‚pi gulmalatātvam, tataś ca śilākāṣṭhaloṣṭatṛṇāditvaṃ gacchantītyarthaḥ

Śrīdhara

idānīṃ sattvādi-vṛtti-śīlānāṃ phala-bhedam āha ūrdhvam iti | sattva-sthāḥ sattva-vṛtti-pradhānāḥ | ūrdhvaṃ gacchanti sattvotkarṣa-tāratamyād uttarottaraṇataguṇānandān manuṣya-gandharva-pitṛdevādi-lokān satya-loka-paryantān prāpnuvantīty arthaḥ | rājasās tu tṛṣṇādy-ākulā madhye tiṣṭhanti | manuṣya-loka eva utpadyante | jaghanyo nikṛṣṭas tamo-guṇaḥ | tasya vṛttiḥ pramāda-mohādiḥ | atra sthitā adhogacchanti | tamaso vṛtti-tāratamyāt tāmisrādiṣu nirayeṣu utpadyante

Madhusūdana

idānīṃ sattvādi-vṛtta-sthānāṃ prāg-uktam eva phalam ūrdhva-madhyādho-bhāvenāha ūrdhvam iti | atra tṛtīye guṇe vṛtta-śabda-yogād ādyayor api vṛttam eva vivakṣitam | tena sattvasthāḥ sattva-vṛtte śāstrīye jñāne karmaṇi ca niratā ūrdhvaṃ satya-loka-paryantaṃ deva-lokaṃ gacchanti te deveṣūtpadyante jñāna-karma-tāratamyena | tathā madhye manuṣya-loke puṇya-pāpa-miśre tiṣṭhanti na tūrdhvaṃ gacchanty adho vā manuṣyeṣūtpadyante rājasā rajo-guṇa-vṛtte lobhādi-pūrvake rājase karmaṇi niratāḥ | jaghanya-guṇa-vṛttasthā jaghanyasya guṇa-dvayāpekṣayā paścād-bhāvino nikṛṣṭasya tamaso guṇasya vṛtte nidrālasyādau sthitā adho gacchanti paścādiṣūtpadyante | kadācij jaghanya-guṇa-vṛtta-sthāḥ sāttvikā rājasāś ca bhavanty ata āha tāmasāḥ sarvadā tamaḥ-pradhānāḥ | itareṣāṃ kadācit tad-vṛtta-sthatve ‚pi na tat-pradhānateti bhāvaḥ

Viśvanātha

sattva-sthāḥ sattv-tāratamyenordhvaṃ satya-loka-paryantam | madhye manusya-loka eva | jaghanyaś cāsau guṇaś ceti tasya vṛttiḥ pramādālasyādis tatra sthitā adho gacchanti narakaṃ yānti

Baladeva

atha sattvādi-vṛtti-niṣṭhānāṃ tāny eva phalāny ūrdhva-madhyādho-bhāvenāha ūrdhvam iti | tamasi vṛtti-śabdād itarayoś ca vṛttir vivakṣitā | sattvasthāḥ sattva-vṛtti-niṣṭhāḥ sattva-tāratamyenordhvaṃ satyaloka-paryantaṃ gacchanti | rājasā rajo-vṛtti-niṣṭhā madhye puṇya-pāpa-miśrite manuṣya-loke tiṣṭhanti | manuṣyā eva bhavanti rajas-tāratamyena | jaghanyaḥ sattva-rajo ‚pekṣayā nikṛṣṭo yo guṇas tamaḥ-saṃjñas tad-vṛttau pramādādau sthitās tv adho gacchanti tamas-tāratamyena paśu-pakṣi-sthāvarādi-yoniṃ labhante | tāmasā ity uktis teṣāṃ sarvadā tamasi sthitiṃ vyanakti