ष्टकृत् ।निरञ्जनः शुचिः ।सिद्धो निर्वृत्तोऽर्थ्यमानोऽर्थोऽस्येति सिद्धार्थः, 'सत्यकामः' इति श्रुतेः ।सिद्धो निष्पन्नः संकल्पोऽस्येति सिद्धसंकल्पः, 'सत्यसंकल्पः' इति श्रुतेः ।सिद्धिं फलं कर्तृभ्यः स्वाधिकारानुरूपतां ददातीति सिद्धिदः ।सिद्धेः साधकत्वात् सिद्धिसाधनः ॥
In plain words
Untouched by any stain, pure, ever-fulfilled and complete, the supreme goal sought by all—he is Siddhārtha, as the scripture declares: 'He whose desires are true.' He whose will never fails is Siddhasaṅkalpa, in the words of the Veda: 'He whose resolve is true.' Because he grants the fruits of action to every seeker in exact accordance with their capacity, he is the giver of success, Siddhidah; and because he is the very means to supreme attainment, he is Siddhisādhanaḥ.
Close to the Sanskrit
Untouched by stain, pure, accomplished, fulfilled, sought after, he whose purpose is attained is Siddhārtha, on account of the shruti text 'whose desires are true'. He whose resolve is accomplished is Siddhasaṅkalpa, on account of the shruti 'whose resolve is true'. Because he grants the fruit of success to doers in accordance with their respective qualifications, he is Siddhidah. Because he is the instrumental cause of perfection, he is Siddhisādhanaḥ.