Their commitment was not determined by circumstances or what other people are doing. Their commitment and conviction was based on who God is to them that their mind was made before the trial and fire ever started.
The 3 hebrew boys are a picture of Psalm 23:4
Psalm 23:4 CSB
Even when I go through the darkest valley, I fear no danger,
God’s Presence in the fire
As a child of God, you will never go through a fire where Jesus is not there with you.
Peace in the Fire
Peace in the fire means you are trusting His promise that He will never leave you nor forsake you no matter the fire you are in.