What Is a True Fast?

Isaiah 58 & the Sermon on the Mount — A 15-Minute Lesson

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What Is a True Fast?

Isaiah 58 & the Sermon on the Mount — A 15-Minute Lesson

Isaiah 58 (NIV) in Dialogue with Matthew 5–7 (NIV)

By PS-Church

Lesson Outline & Timing
0:00–1:30HOOK: The Problem with Religious Performance
1:30–4:00SECTION 1: The God Who Confronts Empty Fasting (Isa 58:1–5)
4:00–8:00SECTION 2: The Fast God Actually Chose (Isa 58:6–7) — The Heart
8:00–11:00SECTION 3: The Promises & the Sabbath (Isa 58:8–14)
11:00–13:30SECTION 4: Matthew 5–7 — Jesus Fulfills Isaiah's Vision
13:30–15:00APPLICATION & CLOSING: What Does Your Fasting Look Like?
HOOK (0:00–1:30) — The Problem with Religious Performance

Ask the Room:

"Have you ever done something spiritual — fasted, prayed, given — and felt like God wasn't listening? Why do you think that happens?"

SETUP: In Isaiah 58, God confronts a people who are doing everything right — fasting, seeking God, humbling themselves — and He says: "I'm not listening." This is the question Isaiah 58 is answering: What does God actually want from us when we fast?

SECTION 1 (1:30–4:00) — The God Who Confronts Empty Religion

Key Verses:

v.1 Shout it aloud, do not hold back. Raise your voice like a trumpet. Declare to my people their rebellion...
v.2 Day after day they seek me out; they seem eager to know my ways, as if they were a nation that does what is right...
v.3a Why have we fasted...and you have not seen it? Why have we humbled ourselves, and you have not noticed?
v.5 Is this the kind of fast I have chosen, only a day for people to humble themselves? Is it only for bowing one's head like a reed?

Two Key Word Studies:

פֶּשַׁע (pesha') — Willful rebellion (v.1)
Not accidental sin — deliberate covenant-breaking. God knows their fasting is not innocent mistake.
אַגְמוֹן (agmon) — A reed / bulrush (v.5)
Bows with every wind but has no moral backbone. God's scalding image of their "humility."

Isaiah 58:1–5 teaches:

  • The people's religion was real but disconnected — genuine practice, empty of transformation.
  • They fasted AND exploited workers on the same day (v.3b). Religion and injustice coexisted.
  • Their "humility" was reed-humility — bending before God on fast days, snapping back to exploitation the next morning.

Matthew Connection:

ISA — v.2: They look righteous, seek God daily, ask for just decisions. Outward compliance without inner transformation.
MATT — Matt 5:20: "Unless your righteousness surpasses that of the Pharisees..." Matt 6:1: Practicing righteousness "to be seen by them."
SECTION 2 (4:00–8:00) — The Fast God ACTUALLY Chose

Isaiah 58:6–7 — The Most Important Verses in the Chapter

vv.6–7

Is not this the kind of fasting I have chosen: to loose the chains of injustice and untie the cords of the yoke, to set the oppressed free and break every yoke? Is it not to share your food with the hungry and to provide the poor wanderer with shelter — when you see the naked, to clothe them, and not to turn away from your own flesh and blood?

Word Studies — The Anatomy of True Fasting:

חַרְצֻבּוֹת (chartsuvot) — Chains, bonds (v.6)
Prisoner's chains. True fasting = liberation of the captive. The fast you do to free yourself should produce freedom for others.
מוֹטָה (motah) — Yoke of burden (v.6)
Heavy wooden yoke of slavery and economic oppression. Yoke-breaking is true fasting.
רְצוּצִים (retsutsiym) — Crushed ones (v.6)
Same word Jesus quotes from Isa 61:1 in Luke 4:18 — his mission statement. Jesus is the ultimate faster.
לַחְמְךָ (lachmekha) — YOUR bread (v.7)
Not surplus — your bread. God demands sacrifice, not charity from excess. True fasting is costly.

THE BIG IDEA:

True fasting is not primarily about what you withhold from yourself — it is about what you release to others. The hunger you feel in fasting is meant to produce solidarity with those who are involuntarily hungry.

The Fast Consists of 6 Actions:

  • Loose the chains of injustice
  • Break every yoke of oppression
  • Share your food with the hungry
  • Provide shelter to the homeless poor
  • Clothe the naked
  • Do not turn away from family/community

Matthew 5–7 Connection:

ISA — Isa 58:6–7: God defines true fasting as liberation, feeding, sheltering, clothing the vulnerable. These are acts done to real people.
MATT — Matt 5:6–7: "Blessed are those who hunger for righteousness...the merciful." Matt 25:35–36: Feeding/sheltering/clothing = serving Christ himself.
SECTION 3 (8:00–11:00) — The Promises and the Sabbath

The Promises of True Fasting (vv.8–12):

v.8 Then your light will break forth like the dawn, and your healing will quickly appear...then you will call, and the Lord will answer...
vv.11–12 The Lord will guide you always...You will be like a well-watered garden, like a spring whose waters never fail. You will be called Repairer of Broken Walls...
הִנֵּנִי (hineni) — Here I am (v.9)
God's own word back to the faithful. Abraham says it to God (Gen 22). Isaiah says it to God (Isa 6:8). Now God says it to the just community.
גַּן רָוֶה (gan raveh) — Well-watered garden (v.11)
Edenic imagery — the community that does justice becomes a restored Eden, a life-giving oasis.
גֹּדֵר פֶּרֶץ (goder perets) — Repairer of Broken Walls (v.12)
The highest honor: the community whose justice practice rebuilds the social fabric of a shattered society.

The Sabbath Capstone (vv.13–14):

vv.13–14 If you call the Sabbath a delight (oneg) and the Lord's holy day honorable...then you will find your joy in the Lord, and I will cause you to ride in triumph on the heights...
עֹנֶג (oneg) — Delight, luxury, pleasure
The Sabbath is not reluctant obligation — it is deep, sensory delight in God. The same word root as Eden's pleasures.

POINT: The Sabbath holds all true fasting together. You cannot sustain liberation, feeding, clothing, and justice without a Sabbath rhythm — a regular stopping of self-directed activity to rest in God.

SECTION 4 (11:00–13:30) — Jesus Fulfills Isaiah's Vision

The Sermon on the Mount as Isaiah 58 Fulfilled

Empty Religion (Performance condemned: reed-humility, bowing head (v.5)) — Matt 6:1 — "Do not practice righteousness to be seen"
True Justice = True Worship (Feeding, sheltering, clothing = acceptable fast (v.6–7)) — Matt 25:35 — Doing it to the least = doing it to Christ
No Contempt (Remove the pointing finger and malicious talk (v.9b)) — Matt 5:22 — Contempt puts you in danger of hellfire
Light as Witness (Light breaks forth; darkness becomes noonday (v.8,10)) — Matt 5:14–16 — "You are the light of the world"
Rest in God (Sabbath as oneg — delight (v.13)) — Matt 11:28–29 — "Come to me and I will give you rest"

KEY CONNECTION: Jesus doesn't just teach Isaiah 58 — He fulfills it. He is the yoke-breaker (Matt 11:28), the bread-sharer (John 6), the one who clothes the naked with His righteousness. The cross itself is the ultimate fast: total self-emptying for the liberation of others.

APPLICATION (13:30–15:00) — What Does Your Fasting Look Like?

Three Diagnostic Questions from Isaiah 58:

1. Performance Check (v.2–5): Are you performing religion or being transformed by it? Is your spiritual practice producing justice, mercy, and humility — or just comfort and self-improvement?

2. The Neighbor Test (v.6–7): Does your fasting/praying produce action toward the hungry, the oppressed, the homeless, the vulnerable? Or does it stay entirely internal?

3. The Hineni Response (v.9a): God says "Here I am" to those who practice justice. If God feels distant, Isaiah 58 suggests asking: Who is the person I have been turning away from?

Closing Challenge:

This week, choose one element of Isaiah 58:6–7 and do it as an act of fasting:

  • Fast a meal and give the money to a local food pantry
  • Identify someone in your community who carries a heavy yoke — and help break it
  • Remove a "pointing finger" — restore a broken relationship
  • Practice Sabbath oneg — stop your own business one morning and simply delight in God

Pleasant Springs Church — Discipleship School

“Your light will break forth like the dawn.” — Isaiah 58:8

“You are the light of the world.” — Matthew 5:14

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