In Matthew 13, Jesus tells a parable about the Kingdom of heaven using a tiny seed.

“The kingdom of heaven is like a mustard seed, which a man took and planted in his field. Though it is the smallest of all seeds, yet when it grows, it is the largest of garden plants and becomes a tree, so that the birds come and perch in its branches.”

The message is clear. God works in small ways to create big changes.

That metaphor is the inspiration for The Mustard Seed.

I think of it this way: even a little grace makes a big difference.

To that end, my deep desire is to help folks come alive to the wonder, beauty, and transforming power of God’s grace by tethering all of life to the cross of the risen and reigning Jesus.

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👋 Meet McKay Caston

Hi, my name is McKay.

After serving twenty-six years as a local church pastor, I now teach on the faculty and lead the Doctor of Ministry program in Gospel Renewal and Pastoral Leadership for Metro Atlanta Seminary.

I also create online resources for Mustard Seed Discipleship.

While I've shifted from pastor to professor and content creator, my passion hasn't changed. The aim of my ministry is to help folks escape religious moralism by coming alive to the wonder, beauty, and transforming power of God's grace in the crucified, risen, and reigning Jesus.

On a personal note, I've been married to Kristy for 30 years, and we have three children, 26, 23, and 18. With B.A., M.Div., D.Min., and Ph.D. degrees, I also enjoy school. 🤓

When not teaching, writing, or creating discipleship content, I enjoy time at home and hiking the mountains of north Georgia.

Our Passion: The Centrality of Substitution

I deeply desire for each resource we produce to renew your heart by encountering the Father’s heart for you, awakening your soul more and more to the height, depth, width, and breadth of his deep, unrelenting love expressed most undeniably through the cross of Christ—that you would live all of life in view of that redemptive story, seeing, savoring, and celebrating the glorious grace of God in Jesus!

The story of redemption is the story of the Bible and of all history. The epicenter of that story is the cross of Christ, where he becomes a substitute for sinners, taking the place of judgment so that we can be forgiven and free.

Dr. Tim Keller says, “The key to spiritual renewal is the continual re-discovery of the gospel.” 

Keeping with that philosophy, the message of the cross looms large in every MSD resource, with the goal being a “continual re-discovery of the gospel." Tethering all of our content to the cross, we long for believers to come alive to the present value of Jesus’ blood.

If there is a word that most encapsulates the theological foundation of the gospel, it is substitution.

This is why every piece of content we produce touches on the concept of “Jesus in my place.” He lived in our place, achieving an actual record of perfect righteousness with which to replace the rags of our unrighteousness and self-righteousness. He also died in our place, satisfying in full the demands of justice our sin deserved. As our sin-bearer and righteousness provider, Jesus is our substitute in life and death. His resurrection serves as confirmation that these extraordinary gospel promises are true.

When someone consciously believes the gospel, the Spirit engrafts them into Jesus like a branch is connected to a vine. Theologically, we call this union with Christ, where we abide in him by faith, believing that Jesus’ perfect righteousness is now our perfect righteousness (our new and true identity). As a believer presses into the vine with a present awareness of the value of Jesus’ blood, the Holy Spirit, like sap from the vine, flows into them, filling the disciple with new desires and abilities, changing me from the inside out.

This cross-centered theology of substitution is the foundation underlying every Mustard Seed Discipleship resource.

Three Core Doctrines Woven into Every Resource

#1 — JUSTIFICATION: Grace-Centered Theology

At the heart of all of Scripture is the redemptive message of God’s saving grace to sinners in Jesus. Theologically, we call this justification, which is the hub of the theological wheel to which every passage and doctrine is connected. This grace message is the oak from which every acorn of biblical text falls and must be related in order to be properly understood and applied. This is why Mustard Seed Discipleship is committed to grace-centered theology. 

"The doctrine of justification by faith through the substitutionary sacrifice of Christ is very much to my ministry what bread and salt are to the table. As often as ever the table is set, there are those necessary things. I regard that doctrine as being one that is to be preached continually, to be mixed up with all of our sermons.”
- Charles H. Spurgeon, Sermon #3488, October 9, 1870

#2 — ADOPTION: Grace-Focused Identity

Every human either will find his or her core identity in a self-achieved righteousness or in a gift-received righteousness. We will functionally live as spiritual orphans trying to make a life and name for ourselves, or we will live like adopted and beloved sons and daughters, with all the freedom, peace, hope, and joy that flows from such an identity. The implications are manifold and wide-ranging, touching on practically every area of life.  This is why The Mustard Seed is committed to grace-focused identity.

“Adoption is the highest privilege of the gospel. The traitor is forgiven, brought in for supper, and given the family name. To be right with God the Judge is a great thing, but to be loved and cared for by God the Father is greater.”
— J.I. Packer

#3 — SANCTIFICATION: Grace-Empowered Transformation

What now? Should I expect to experience a spiritual change in my life? If so, how does that take place? What is my role in the process?  As Jesus says in John 15, “No one can produce good fruit apart from me.” Practically speaking, this means that we experience the fruit of the Spirit as we consciously abide in the Vine of Jesus’ imputed gift-righteousness. As the Spirit fills us like sap through a vine into a branch, we receive new motives and a new ability to manifest the new life of love, peace, patience, kindness, etc. This is why The Mustard Seed is committed to grace-empowered transformation.

“It is by simple, close, and searching views of the cross of Christ that the Spirit most effectually sanctifies the believer. This is the true and great method of gospel sanctification! Let no man dream of true mortification of sin, or real sanctification of heart, who does not deal constantly, closely and believingly with the atoning blood of Jesus.”
— Octavius Winslow, The Work of the Holy Spirit (129)

🧱 Our Theological Foundations

The Bible

The Bible is God’s special revelation to humanity, centering on the glory of God’s grace through the life, death and resurrection of Jesus. Therefore, as the word of God, the Bible alone is our ultimate authority for all of life, theologically, devotionally, and practically. 


People are reconciled to God, not by their own good works, but through faith alone in the good works of Jesus. Therefore, someone becomes a Christian not by doing for God, but by receiving from God. 


Salvation being through faith alone means that people are reconciled to God by grace alone through the voluntary, vicarious, substitutionary death of Jesus. Therefore, the Christian’s standing before God is a gift, not a reward. 

Jesus Christ

Our only hope of forgiveness, righteousness, and eternal life is gained through the life, death, and resurrection of Jesus Christ, not by any merit or effort of our own. 

The Glory of God

The goal of our theology is that God alone would receive the glory for redeeming, adopting, and empowering sinners with new life. Therefore, there is no room for self-righteousness in the gospel, but only for boasting in the cross of Jesus. 

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Helping folks come alive to the wonder, beauty, and transforming power of God's grace by tethering all of life to the cross of the risen and reigning Jesus.


Because even a little grace makes a big difference.