In plain words
Tapas performed for honour, respect, and worship, and out of hypocrisy, is called rājasa: it belongs to this world, is unstable, and is inconstant in its fruit.
Word for word
The tapas which is done for honour, respect and worship, and indeed with hypocrisy: that is declared here [to be] rājasa, unsteady, inconstant.
सत्कारमानपूजार्थं तपो दम्भेन चैव यत्क्रियते तदिह प्रोक्तं राजसं चलमध्रुवम्
Other commentaries
The commentators
▸Bhagavadgītābhāṣyam· bhāṣya
सत्कारः साधुकारः ‘साधुः अयं तपस्वी ब्राह्मणः’ इत्येवमर्थम् , मानो माननं प्रत्युत्थानाभिवादनादिः तदर्थम् , पूजा पादप्रक्षालनार्चनाशयितृत्वादिः तदर्थं च तपः सत्कारमानपूजार्थम् , दम्भेन चैव यत् क्रियते तपः तत् इह प्रोक्तं कथितं राजसं चलं कादाचित्कफलत्वेन अध्रुवम् ॥ १८ ॥
In plain words
'Honor' means the approval that sounds like, 'ah, what a virtuous, austere brahmana this is' -- and that is exactly what people are after. 'Esteem' means the respect shown by others rising for you, greeting you, and the like -- that is what they want. 'Worship' means having your feet washed, being venerated, offered a seat -- that too is the goal. Austerity performed for the sake of honor, esteem, and worship -- and equally, austerity done out of pure hypocrisy -- all of that is declared here to be rajasic: unsteady, because whatever it produces never lasts.
Close to the Sanskrit
'Satkara' [means] approval, [as in] 'this is a virtuous, austere brahmana' -- for this very purpose; 'mana' [means] respect, [shown by] rising up, salutation, and so on -- for that purpose; 'puja' [means] washing the feet, honoring, offering a seat, and so on -- for that purpose too; austerity for the sake of honor, esteem, and worship; and, whatever austerity is done out of hypocrisy indeed -- that austerity, here, is declared, stated, [to be] rajasic, fickle, because of the impermanence of its fruit, unstable.