In plain words
Having created beings together with yajña, Prajapati said of old: By this shall you prosper; let this be for you the fulfiller of cherished desires.
Word for word
Having created beings together with yajña, of old Prajāpati said: by this you shall multiply; let this be for you the yielder of desired wishes.
सहयज्ञाः प्रजाः सृष्ट्वा पुरोवाच प्रजापतिःअनेन प्रसविष्यध्वमेष वोऽस्त्विष्टकामधुक्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam
इतश्च अधिकृतेन कर्म कर्तव्यम् —
सहयज्ञाः यज्ञसहिताः प्रजाः त्रयो वर्णाः ताः सृष्ट्वा उत्पाद्य पुरा पूर्वं सर्गादौ उवाच उक्तवान् प्रजापतिः प्रजानां स्रष्टा अनेन यज्ञेन प्रसविष्यध्वं प्रसवः वृद्धिः उत्पत्तिः तं कुरुध्वम् । एष यज्ञः वः युष्माकम् अस्तु भवतु इष्टकामधुक् इष्टान् अभिप्रेतान् कामान् फलविशेषान् दोग्धीति इष्टकामधुक् ॥ १० ॥
In plain words
And here is a further reason why the one who is qualified must act —
'Together with sacrifice' simply means accompanied by sacrifice — meaning the creatures, the three upper castes. Having created them, long ago, at the very start of creation, Prajāpati spoke — Prajāpati, the creator of all creatures. He said, 'through this sacrifice, may you multiply' — prasava here means growth, increase — go and bring that about. And he said, 'may this sacrifice become for you the cow that yields your desires' — it milks out, gives forth, whatever you truly want, particular fruits exactly as desired. That is what 'yielder of desired wishes' means.
Close to the Sanskrit
And from this too, action is to be performed by the one who is qualified —
'Together with sacrifice' [means] accompanied by sacrifice — [i.e.] creatures, the three [upper] castes; having created, having produced, them, of old, formerly, at the beginning of creation, Prajāpati said, spoke — Prajāpati, the creator of creatures. 'By this sacrifice, may you multiply' — prasava [means] growth, [i.e.] increase; that, perform. 'May this sacrifice be, become, for you, the yielder of desired wishes' — [it] milks, yields the desired, the intended wishes, [i.e.] particular fruits — that is [the meaning of] 'the yielder of desired wishes'.