The second definition reflects the effort to which those of great moral character will go to maintain that character.  Why would we do such a thing?  I consider the words of the Master:

"For what will it profit a man if he gains the whole world and forfeits his soul? Or what will a man give in exchange for his soul?  (Matthew 16:26)

This word presents a challenge for believers.   Are we scrupulous in our morality and in our service and devotion to G-d?  Here are M-W's notes regarding the etymology of the word:

"Scrupulous" and its close relative "scruple" ("an ethical consideration") come from the Latin noun "scrupulus," the diminutive of "scrupus." "Scrupus" refers to a sharp stone, so "scrupulus" means "small sharp stone." "Scrupus" retained its literal meaning but eventually also came to be used with the metaphorical meaning "a source of anxiety or uneasiness," the way a sharp pebble in one's shoe would be a source of pain. When the adjective "scrupulous" entered the language in the 15th century, it meant "principled." Now it also commonly means "painstaking" or "careful."

A sharp stone?  This brings to mind some passages of Scripture:

Then Zipporah took a flint and cut off her son's foreskin and threw it at Moses' feet, and she said, "You are indeed a bridegroom of blood to me."  (Exodus 4:25)

And a similar story involving flint in Joshua 5:3

So Joshua made himself flint knives and circumcised the sons of Israel at Gibeath-haaraloth.

What about sharp iron?

Iron sharpens iron, So one man sharpens another.  (Proverbs 27:17)

Other thoughts on this:

For we are His workmanship, created in Christ Jesus for good works, which God prepared beforehand so that we would walk in them.  (Ephesians 2:10)

Here is the perseverance of the saints who keep the commandments of God and their faith in Jesus.  (Revelation 14:12)

May He who is the Source of all good things give us the strength and courage to remain steadfast and scrupulous in our walk before Him.