It looks to me like it DOES matter what is on the outside.
It isn't just the heart.
Why would we want to boast that it is the heart that matters anyway?
Jeremiah 17:9 The heart is deceitful above all things, and desperately wicked: who can know it?
10 I the LORD search the heart, I try the reins, even to give every man according to his ways, and according to the fruit of his doings.
- Search me, O God, and know my heart today,
Try me, O Savior, know my thoughts, I pray;
See if there be some wicked way in me;
Cleanse me from every sin, and set me free.
What others see.