As far back as I can recall, Christians have utilized the phrase, "personal relationship" in evangelism. It is oft-times used as a synonym for "salvation." Perhaps pressing the phrase to its unlikely meaning, we might suggest that the phrase, "personal relationship" includes one's union with Christ, justification, sanctification, reconciliation, and eventual glorification. At a minimum, if the former is meant by the phrase, it seems like an acceptable set of words to utilize in evangelistic outreach.
The problem I have with the phrase, however, is not which theological categories it includes but which categories it obviously does not. I can only base my observations on personal experience, but I have yet to hear testimony, whether while witnessing or some other published work/blog/Facebook post/Tweet, that the "personal relationship" language epidemic includes both the wrath of God and the Church.
The Wrath of God
While believers (i.e., Christians) have a reconciled relationship with God through Jesus Christ, unbelievers do not. Despite this contrast, unbelievers, nevertheless, have a personal relationship with God. In fact, it is an extremely intimate relationship. It is one of strife, enmity, and hostility (Rom. 8:6-8). The Lord knows their every thought, word, and deed (Ps. 14:2-3). He knows their sin and guilt, and he will no by means clear the guilty (Exod. 34:7). This relationship travels in two directions, however.
As the Westminster Catechism suggests, "There is but one only, the living and true God" (WSC 5). Unbelievers know this God because the work of the law is written upon their hearts (Rom. 1:18-23; 2:14-15); they are made in his image and after his likeness (Gen. 1:26-27; 5:3), and his glory is constantly declared to them in the heavens above (Ps. 19:1-6). The scriptures even suggest they hate God (John 15:18-25).
From both perspectives (i.e., God and the unbeliever), therefore, the personal relationship that exists is one of of wrath. God's wrath abides upon the unbeliever (John 3:36) and the unbeliever hates God (Rom. 8:7).
Like many things in the United States and other parts of the world, ideas are personalized. Those in marketing desire to tailor-fit their product to individuals. "You" in advertising campaigns is most often utilized in the second person singular.
Similarly, one might make the same claim about the phrase, "personal relationship." It is an individualized phrase that makes salvation solely personal. But is it? On the one hand, it is. No one will be saved based on the faith of another. Individuals are called to repent and believe upon Jesus Christ (Acts 17:30-31). Yet, while we are saved based on the righteousness of Christ imputed to us individually, we are not saved to remain individuals. As I have put it elsewhere, we are not saved to be spiritual nomads. We are saved, among many things, to become a part of a community, the Church. God calls us to serve each other in various ways (1 Cor. 16:1-2; Heb. 10:24-25), submit to church leadership (Heb. 13:17), attend to the means of grace (Matt. 28:16-20; Acts 2:42), etc. etc. This is done in community; this is done in and as a church.
If the phrase, "personal relationship" does not include these important categories, should we consider altering, perhaps no longer using, it?
Although I have not given this much thought, if we want to continue using similar phrases, perhaps we should use, "saving relationship"? Instead of telling people they need a personal relationship, we could tell them that they need a saving relationship. That may beg the question, "saved from what?" The answer: God's wrath. Digging a bit deeper, it could also elicit the question, "saved with whom"? The answer: the Church.
Even if those questions are not raised by the unbeliever, Christians can just as easily answer those questions for the unbeliever as they share the good news of Christ and declare, "You need a saving relationship with God"!