Kartitva bhava is sin

 Idea of doership is sin.

With kartitva , bhoktritva comes

Effects of karma follow.

Idea of doership stems from ignorance and ignorance alone.

To have an idea of doership you have to believe in the concept of an entity.

Bound is he who clings on to the concepts of an entity and a world

which for a dnyani of course do not exist.

Says Mundaka upanishad;

Kshiyan techasya karmaani

tasmin drishte paravare

The 3 karmas sanchit, prarabdha and agami burn to ashes 

On knowing Reality.

When avarna is gone, para is revealed.

Such a soul need not worry about millions of karmas

Says Shankaracharya.

Nahi dnyane na sadrusham pavitramahi vidyate Gita 4.38

Nothing is as pure as knowledge.

By knowing, one transcends.

Knowing results in mukti

Sa vid ya vimuktaye.

And nothing else.

A man who has come to such a mature understanding

chooses dnyan

as his purifier.

Knowing that dnyan alone can redeem him

not karma.

Na karmana prajena dhanena tyagenaike amruta tattva manushaha

Not by karma, but by getting rid of the obsession to perform it, will you walk on the subtle path to Atma dnyan.

Not by being born in a noble. pious family, not by gifting a thousand cows. not by performing 100 yadnyas will you get enlightened, but by naturally understanding, that none of these things contribute to self knowledge.

However, until our understanding is thus purified, one should continue doing these, lest he falls in bad company and does self destructive deeds.