But the fruit of the Spirit is love, joy, peace, patience, kindness, goodness, faithfulness, gentleness, self-control; against such things there is no law. (Galatians 5:22-24)
Peace is a cousin to joy, and swims in stiller, deeper waters. Rather than simply being the absence of war, or of strife, peace also points to a state of wellbeing. It is a deep calmness which withstands the buffets of waves, and the whirling winds of anxiety.
This peace is not founded on material goods, but rather a deep dependance upon God. It is nurtured by prayer, and the ability to trust God with the results of that prayer. Because of this, it is commonly a peace which is at odds with your physical circumstance. Paul puts it well:
Rejoice in the Lord always; again I will say, rejoice. Let your reasonableness be known to everyone. The Lord is at hand; do not be anxious about anything, but in everything by prayer and supplication with thanksgiving let your requests be made known to God. And the peace of God, which surpasses all understanding, will guard your hearts and your minds in Christ Jesus. (Philippians 4:4–7)
It is this peace which emboldened the martyrs of the church, and enabled others to face trial and tumult. It is the ready turning to prayer, and the habit of trust in a God who is over all. It is a fruit of trust. The well known hymn puts it well:
When peace like a river attendeth my way,
When sorrows like sea billows roll;
Whatever my lot Thou hast taught me to say,
“It is well, it is well with my soul!”
Though Satan should buffet, though trials should come,
Let this blest assurance control,
That Christ hath regarded my helpless estate,
And hath shed His own blood for my soul.
My sin—oh, the bliss of this glorious thought—
My sin, not in part, but the whole,
Is nailed to His Cross, and I bear it no more;
Praise the Lord, praise the Lord, O my soul!
For me, be it Christ, be it Christ hence to live;
If dark hours about me shall roll,
No pang shall be mine, for in death as in life
Thou wilt whisper Thy peace to my soul.