Teshuvah measured against intent

איתא האומר אחטא ואשוב אין מספיקין בידו כו'.

It is taught: One who says, "I will sin and then do teshuvah," they do not grant him the opportunity to do teshuvah.

Chazal (Yoma 85b) teach that a person who plans to sin while relying on teshuvah afterward is not given Heavenly help to repent — his cynical use of teshuvah as a license to sin removes the very assistance teshuvah depends on.

הטעם כיון שקלקל ע"י התשובה לכן אין מספיקין בידו.

The reason is that since he has corrupted the matter through teshuvah itself, therefore they do not grant him the opportunity.

The Sefas Emes explains the principle: because the man has misused the holy power of teshuvah as a tool for sinning, that same power is withheld from him — the means he abused is taken away.

ויש ללמוד מזה ג"כ למי ששב בתשובה על ידי יראת חטא שירא פן יכשילהו היצה"ר שנית.

And one can learn from this as well regarding someone who returns in teshuvah out of yiras cheit (fear of sin) — that he fears lest the yetzer hara cause him to stumble a second time.

The same rule, reversed, applies to a sincere baal teshuvah: his teshuvah is driven by a genuine dread of the yetzer hara tripping him up again, the very opposite of one who plans to sin.

נמצא ע"י החטא שב בתשובה.

It emerges that through the sin he returned in teshuvah.

For such a person the earlier sin actually became the catalyst that awakened his teshuvah, since the fear of repeating it drove him back to Hashem.

אין מספיקין בידו לחטוא ומצילין אותו מן החטא כנ"ל:

They do not grant him the opportunity to sin, and they save him from sin, as above.

Measure for measure, just as the cynic is denied teshuvah, the sincere penitent is denied the chance to sin — Heaven actively protects him from stumbling again.

Summary: The Sefas Emes reads the maxim "I will sin and repent" in both directions: one who exploits teshuvah to sin is denied teshuvah, while one whose very fear of sin drives his teshuvah is, measure for measure, guarded by Heaven and saved from sinning.