Sincerity is not enough. You have to do the right thing.
You might be truly sincere about your generosity and your mitzvahs, but if it doesn’t reach the right place, or was not done the right way, it still did not succeed.
Why is it this way? Why can’t we be judged by our intentions alone?
So that we will know that we are small, and Truth is very large. It is Truth that stands at the center, and we that orbit about it.
Tanya, chapter 38. Likutei Sichot vol. 15, pg. 247. Maamar V’Shavti B’Shalom 5738