The Midrash:

“For whoever does work upon it (Shabbat)” (Exodus 31:14) — provided that one does a complete act of work. But suppose one writes one letter in the morning, and another towards evening; or if one wove one strand in the morning and another towards evening, I might think that this person is liable. Therefore, it is written, “For whoever does work upon it” — provided that one does a complete act of work.

Mekhilta d’Rabbi Ishmael, Shabbata, on Exodus 31:12-17 (6 of 13)

Understanding the Midrash:

God created the whole world and then rested. On Shabbat we too rest from “completing” work. We might still (by accident?) do partial labor, but we need to avoid or resist the urge to finish things on Shabbat. Shabbat is a day for acknowledging the hidden wholeness, even when we might feel we are in a state of in-betweenness on projects (as we almost always are).

The prohibition on writing counts with a minimum of two letters. In other words, one letter isn’t a full act of work, and likewise with one woven strand. But two becomes full. If you do two, but not consecutively, it doesn’t count as a full act according to this midrash. One letter, one strand, is simply one, but two begin to add up to much more than their sum. They start to reveal that the work has a goal.

The leniency here reveals that the prohibition of work isn’t simply about the process of work, but the product. When we are in a productive mode, we are oriented towards completing our projects. Shabbat shifts us from productive mode, where we are goal-oriented and looking to achieve deliverable results, to appreciation mode, where existing is its own reward.

An Interpretation:

For me, I love being creative on Shabbat. The lesson I personally draw from this midrash is that when I do work that might traditionally be forbidden on Shabbat, I will seek to do it for its intrinsic worth, trying to achieve a flow state of mindful presence, and limiting any need or desire for my work to have an end result.