Sister, Keep Your Heart While You Train

Rubber and Lysol meet me at the door. Bright fluorescent lights illuminate the rows of steel machines and neatly stacked weights. Windows to the street line one wall, mirrors on the other—a place to watch and be watched.

In this quiet morning hour there’s no one else here. On the other side, where we train for martial arts, stretches a large open space. Heavy bags hang along the back wall, and the rubber mats lie waiting. Soon we’ll step onto those mats to learn a new technique.

Health and fitness for women land on our already crowded to-do lists.

Pack lunches.

Sign school forms.

Plan pickups from practice, drop-offs for birthday parties.

Grab the groceries (what was it we needed again?!)

Prepare for Bible study

And somewhere between the chaos and the calling, we try to stay healthy. Join a gym. It’s what everyone else does, right? 

So we tell ourselves it’s good for us and set out on our fitness journey.

But sister, there’s a danger lurking. 

You won’t find it in the unlit corners, tucked under the weight bench or between sets. The invisible hazard stays buried deeper than that.

We discover the threat only by looking inward, searching the thoughts and attitudes of our hearts.

Examine Your Motives

There’s something wonderfully satisfying when you’ve finished a workout. You’re sweaty, panting and wrung out with a sense of accomplishment. Your muscles are grateful for the movement, your body responds with endorphins and cortisol and there’s a general sense of confidence and wellbeing.

In David Mathis’ new book, A Little Theology of Exercise, he writes, “Exercise makes happier humans, and God made humans to be happy—in him—with bodily movement being an assistant, rather than an adversary, to Christ-exalting joy.” [1] Caring for our bodies improves our mood, and stewarding the image God gave us leads us to deeper joy in Christ.

It’s a good thing. Until it’s not.

Even good things can become idols. God designed them to be temporary signposts, not ultimate ends. So when we consider our reasons for going to the gym, the answer requires honest self-examination. In the quiet corners of our heart lies a box of unexamined beliefs and buried longings.

We struggle to feel accepted.

“Going to the gym makes me feel popular. Everyone at work goes here.”

We envy what others have.

“I wish I looked like her.”

Or, we fit the cultural ideal—and we like it.

“When I’m at the gym, people notice me and I feel proud to look good.”

We measure ourselves against others.

“She’s lifting more than I am—I need to catch up.”

We seek rest apart from God.

“If I can just push harder here, maybe I’ll feel peace.”

Are we surprised—or too embarrassed—to say it out loud?

But sister, we know “the heart is deceitful above all things” (Jer. 17:9). One of the best deterrents of sin is remembering this truth. Temptation is the bait, sin is the hook that may snag us anytime we find our eyes fixed on that sparkling, mouth-watering lure. 

John Flavel explains, “The greatest difficulty in conversion is to win the heart to God; and the greatest difficulty after conversion is to keep the heart with God.” [2]

That little phrase—keep the heart—became a Puritan shorthand for the Christian’s daily work. As Scripture teaches, “Keep your heart with all vigilance, for from it flow the springs of life’"(Prov. 4:23). This means preserving the soul’s Godward frame and guarding it from sin so it’s fit for communion with God. In other words, not only saying no to sin but saying yes to God.

What does that mean on a Tuesday at the gym?

Explore Your Weaknesses

I’ve seen the destructive nature of this issue in the lives of people in our small town. There’s only a handful of gyms, friends and colleagues are at each of them. But I didn’t expect to hear that each one seemed to hold a story of broken vows or hidden affairs. That fact alone shouldn’t surprise me, but my heart began to crumble as I listened further—brothers and sisters in Christ were part of these stories.

If you’ve walked with believing friends who struggle in their marriage, you know the shock and heartache of this journey—the complexity of hurt and sin in a relationship. There’s never just one piece of the puzzle to solve; it’s all 500 pieces. And suddenly, the picture starts to look uncomfortably familiar.

I find myself quietly asking, "Could that have been me?" Maybe you do too.

There’s no particular reason to fear. My own marriage isn’t perfect, but there’s peaceful assurance in our walk with the Lord, our church community, and close Christian friendships. Our covenant love before God and each other feels steady—but those couples who drifted probably once felt that same confidence too, right?

Guarding our hearts begins here. Bringing what’s secret into the light is a gift from the Holy Spirit, even if it doesn’t feel that way at first. Joel Beeke warns, "If you would avoid entering into temptation, labour to know your own heart." [3]

Opening that box of desires drives us to God because, as Brian Hedges writes, “the only way to kill sin is to mortify the roots of sin in the motives, desires, and drives of the heart.”² Keeping our thoughts and feelings boxed up may not yet be sin, but what we do next is born from them.

“Then desire when it has conceived gives birth to sin, and sin when it is fully grown brings forth death” (Jam. 1:15). Our behavior flows from what’s inside. What fills the heart will eventually find its way out.

We’ll compete and compare. We’ll show up only for those we admire. We’ll dress to impress.

It unfolds slowly, almost without our knowing—and that makes the danger even greater.

When pride, lust, or envy begin to wander through our hearts, they soon take over. It’s like burning something in the microwave—the smoke fills the room, and you have to throw open a window to clear the air.

We air them out by paying attention, by bringing them to God in prayer, by surrendering what tempts us, and by letting the Holy Spirit remind us of truth: “For the word of God is alive and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart” (Heb. 4:12).

You might notice shame starts to tell a different story. It tries to resolve the discomfort by urging you to shove those thoughts and feelings back into the box so no one will see or know.

Consider that God already knows the secrets of our hearts (Ps. 44:21), and holding onto them keeps us from living fully in Christ. For “If we confess our sins, he is faithful and just to forgive us…” (1 John 1:9).

We offer up what we’re afraid to acknowledge and find grace and mercy in the loving care of a faithful God.

God gives us the gift of repentance so we can turn from sin toward holiness. Day by day, step by step, we grieve what draws us away from Christ and glory in His grace, becoming more like Him as He transforms us from within.

Make a Plan

Sister, what will you do now, as you keep your heart before the Lord?

When you’ve unearthed motives and desires, confessed, and repented, it’s time to make a plan. Scripture urges us, “But as for you…flee these things” (1 Tim.6:11).

Involve another.

Grab an accountability partner. Let her in on your struggle—she will understand. Ask her to hold you accountable, and give her permission to ask the hard questions.

Guard yourself.

Identify practical changes that help you flee temptation and pursue holiness.

Is going to that gym the only way to exercise? Could you join a women’s class, work out at home, or attend with friends? Boundaries may be wise—but guarding your heart is more than managing your surroundings. It’s asking the Spirit to redirect our disordered desires, to make love for Christ stronger than the pull of sin.

Confess, grieve, and repent of your sin; then receive the forgiveness we have in Christ. Hold onto the rhythm of self-examination woven into your regular time in the Word and prayer—it’s how you keep your heart steady before Him. 

Pray.

First and foremost, pray for grace to resist worldly temptations. As Joel Beeke reminds us, “Keeping ourselves from entering into temptation is not a thing in our own power…we are to pray that we might be preserved from it because we cannot keep ourselves." [4]

Remember Jesus' instructions in the Lord’s Prayer: “And lead us not into temptation, but deliver us from evil” (Matt. 6:13). Later, He reminds His disciples, “Watch and pray that you may not enter into temptation. The spirit indeed is willing, but the flesh is weak” (Matt. 26:41).

Your Daily Reps

Taking care of our bodies is important, but it’s not of first importance.

We all face sin and temptation daily. It’s no surprise. But perhaps our attention to them is the very way God teaches us to keep our hearts.

We arrive at the gym to strengthen bodies; God calls us to strengthen watchfulness. Reps and routines matter, but the greater workout is guarding what we love. This is the overarching task of our Christian lives—to guard our hearts not only by saying no to sin, but by saying yes to the things of God.

Lord, teach me to guard my heart with diligence and delight, that my strength—body and soul—would bring You glory.

As you care for your body this week, how might you also train your heart toward holiness?

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[1] David Mathis, A Little Theology of Exercise, p.2

[2] Matthew Bingham, A Heart Aflame for God, ch.1

[3] Joel Beeke, Thriving in Grace, ch.10

[4] Beeke, ch.10