“Ki karov elecha hadavar me’od b’ficha ubelevevcha la’asoso”
1. The gemara (Nedarim 51) writes that if one took a neder from food which is “yoreid l’kedeirah” one cannot eat food cooked in an ilfas – the ilfas is used for the finishing stages of food preparation for items that were already “yoreid l’kedeirah”, previously cooked in a kedeirah, and therefore this food is prohibited. However, one who takes a neder from food “na’asah b’kedeirah” is allowed to eat food which is “na’asah b’ilfas”, and if one takes a neder not to eat “na’asah b’ilfas” one is allowed to eat food “na’asah b’kedeirah”. Why here don’t we say that food prepared in an ilfas was previously “na’aseh b’kedeirah” and therefore also prohibited?
Ran answers that the key here is the word “na’aseh”, which refers specifically to the final stage of food preparation. Food prepared in an ilfas was already cooked in a kedeirah, it was “yoreid l’kedeirah”, but it cannot be described as “na’asah b’kedeirah” because the finishing touches were done in an ilfas, not a kedeirah.
2. The mitzvah of tshuvah is multifaceted. Kiddushin 49 tells us that a rasha who is mekadesh a women on condition that he is a tzadik has accomplished effective kiddushin because we assume that a thought of tshuvah passed through his heart -- that fleeting thought of regret means he can no longer be called a rasha. Yet, on the other hand, the Rambam seems to define viduy, a verbal confession as integral to tshuvah if not the very definition of the mitzvah – “viduy zeh mitzvas aseh” (Hil Tshuvah 1:1). Rabeinu Yonah in Sha’arei Tshuvah goes into more detail describing many steps to the tshuvah process.
3. If we consider the many steps involved in complete tshuvah it becomes hard to understand how the mitzvah can be described as ki karov elecha, easy to do. It becomes hard to understand “Tashev enosh at dakah – at dikdukah shel nefesh”, how even till the last breath one can do tshuvah, when tshuvah emands "b'picha", a verbal expression of viduy to be effective.
Therefore, explains R’ Yosef Engel, the pasuk ends “b’levavcha la’asoso”. True, tshuvah with viduy done b’ficha is the ideal, but if we look at what is the most essential ingredient of tshuvah, the final, most crucial step in tshuvah, the “la’asoso” of tshuvah, as the Ran explain, the finishing touch, then we need only focus on the lev, "b'levavcha la'asoso".