As a missionary, my grandfather taught Greek and Hebrew at a seminary in Igbaja, Nigeria. He labored for years after on a cognate lexicon of New Testament Greek. Such interest in biblical languages may sound heady and high-brow, the sort of thing that wouldn't have much connection with vibrant faith.
But nothing could be further from the truth. If you talked to my grandfather about Greek, you'd quickly learn that what he was most passionate about was what he referred to as the "identification truths"--the wide variety of Greek constructions that the New Testament uses to describe Christians' connection with their Savior and Lord Jesus Christ.
Believers are "crucified with Christ" (Gal. 2:20, NIV), "raised with Christ" (Col. 3:1), "in Christ Jesus" (Php. 1:1), "baptized into Christ Jesus" (Rom. 6:3), "sanctified in Christ Jesus" (1 Cor. 1:2), "circumcised by Christ" (Col. 2:11), and reconciled to God "through Christ" (2 Cor. 5:18). Christ's disciples are related to Him as branches to the life-giving vine (Jn. 15:5). In Christ, believers receive "every spiritual blessing" (Eph. 1:3), including election (v.4), predestination (v.5), adoption (v.5), grace (v.6), redemption (v.7), and the sealing of the Holy Spirit (v.13).
This is just a sampling of the Scripture's teaching on the significance of union with Christ for believers. Recent years have seen numerous books tracing and expounding this biblical theme, a renewed focus on what has always been at the heart of Christian faith: the saving relationship that Christians have with their Triune God and Savior, found in the Father's gracious gift of union with the Son by the Spirit. This is core Christianity, in all its warmth and wonder and power.
Christian life is life in Christ. The wonderful truth about Christians' union with Christ, and all that it means, is at the heart of Christianity spirituality. We can probe it in reverent exegesis of the Greek New Testament and we can embrace it with the childlike faith of 'receiving Jesus into your heart.' One thing we cannot do is comprehend the totality of God's kindness to us in Christ.
And one thing we must not do is downplay the significance of this majestic spiritual truth. But there are, tragically, some who call themselves Christians but seek to do just that.
Some months ago, in a bout of tweets responding to The Statement on Social Justice & the Gospel, Union Theological Seminary expressed their rejection of Christ as the only way of salvation. They still claim to be Christians, but they deny that a relationship with Jesus is necessary in order to be saved. Instead, they say:
"We deny that salvation is only found through Christianity, that God's salvific grace is exclusive to any single faith or religion. Moreover, in God's eyes there is no difference in spiritual value or worth between those who are 'in Christ' and those who aren't."
This is a denial of the gospel. Union has denied the union that makes a Christian Christian. The central proclamation of Christianity is that salvation is found in Jesus Christ, and in Him alone. Christians are those who declare that "Jesus is Lord" (Rom. 10:9). The Christian message declares that "Salvation is found in no one else, for there is no other name under heaven given to mankind by which we must be saved" (Acts 4:12).
With tragic logic, Union's denial of the exclusivity of Christ brings a denial of the glory of being included in Christ. Union avers, but for believers there is nothing more precious or significant than their union with Christ by faith through the indwelling of the Holy Spirit. All the wonders of redemption are wrapped up in this notion of being in Christ.
What "spiritual value" comes from union with Christ? It is our position in Him that makes His death count for us and His resurrection mean our life (Rom. 6). Inclusion in Christ is the logic of salvation; when you exclude it from your picture of redemption (even with the intent of being more inclusive), you sever salvation from its source. There is no life apart from Christ. In the oft-quoted words of John Calvin,
"First, we must understand that as long as Christ remains outside of us, and we are separated from him, all that he has suffered and done for the salvation of the human race remains useless and of no value for us. Therefore, to share with us what he has received from the Father, he had to become ours and to dwell within us."
Christianity means we are in Christ, and Christ is in us by the indwelling Spirit.
In God's eyes, those who are in Christ have a whole new identity: "if anyone is in Christ, the new creation has come: The old has gone, the new is here!" (2 Cor. 5:17). What does the new identity of believers look like? Peter declares to believers--"all of you who are in Christ" (1 Pet. 5:14)--that "you are a chosen people, a royal priesthood, a holy nation, God's special possession, that you may declare the praises of him who called you out of darkness into his wonderful light" (2:9).
In these images, picking up on the special status of ethnic Israel in the Old Covenant, Peter describes the privileged status given to believers in Christ in the New Covenant. They are chosen by God from the nations. They have the dignity of both the regal and priestly offices--doubly set apart. They are precious to God, uniquely His. They have a commission of worship and a destiny of glory. All of this is true of every Christian--all those who are united with Christ by faith. None of this is true of those who are not in Christ.
The glory of redemption, the offer of the gospel, is radically inclusive: anyone who will come to Christ will be saved, and receive in Him every spiritual blessing. But the gospel is also utterly exclusive: only in Christ will anyone be saved. There is one way to God, one gate to the kingdom, one bridge from death to eternal life--and that is Christ.
What difference does union with Christ make? All the difference in the world. All the difference in this world, and in the world to come.
 Union Theological Seminary, via Twitter, @UnionSeminary, Sept. 5, 2018.
 Calvin, Institutes of the Christian Religion, III.I.1.
Josh Steely is the Pastor of Pontoon Baptist Church in Pontoon Beach, IL.