The lines “I had to drop the armful in the road / And try to stack them in a better load” contribute significantly to the overall meaning of the poem by illustrating the speaker's recognition of their limitations and the need to reassess their approach. They highlight the idea that sometimes, in order to move forward effectively, one must let go of certain burdens. This aligns with the interpretation that the speaker acknowledges the necessity of leaving some things behind to achieve a more manageable and efficient way of carrying their load.
Therefore, the most fitting interpretation would be:
These lines build on the idea that the speaker has recognized that in order to complete their task they might need to leave some things behind.
This interpretation underscores a theme of self-awareness and the importance of adaptability in the face of challenges.