Is the “kingdom” the same as the “church”? The answer to this question is both “yes” and “no.” In some places “church” and “kingdom” are virtual synonyms. In other passages “church” and “kingdom” do not mean the same thing.
Jesus said His people would partake of the Lord’s Supper in the “kingdom” (Mt. 26:29) and Paul said this activity is done in the “church” (1 Cor. 11:20-22). In Mt. 16:18 Jesus spoke of the “church” and then immediately spoke of the “kingdom” (Mt. 16:19). Paul said the saved are “translated into the kingdom” (Col. 1:13) and then spoke of the “church” just a few verses later (Col. 1:18). In this same book he referred to “fellow workers in the “kingdom” (Col. 4:11) and then spoke of the “church” (Col. 4:15-16). Paul wrote to the “church” at Thessalonica (1 Thess. 1:1) and then said these Christians had been “called into the kingdom” (1 Thess. 2:12). The Hebrew writer spoke of the “church” (Heb. 12:23) and then said these saints had access to the kingdom (Heb. 12:28). Jesus’ blood purchased a “kingdom” (Rev. 5:9-10, ASV), but Acts 20:28 says Jesus’ blood purchased the church.
Just as there are different words in the New Testament that describe “elders” to describe different facets of an elder’s work (compare Tit. 1:5 with Tit. 1:7), so “kingdom” and “church” are sometimes used in this same way.
While many passages do use “kingdom” and “church” interchangeably, these two words are not always identical. In Mt. 8:12 when Jesus said “but the sons of the kingdom shall be cast forth into the outer darkness: there shall be the weeping and the gnashing of teeth” He clearly was not referring to the church. Satan has a “kingdom” (Mt. 12:26), but this kingdom is certainly not the church. At the end of time when Jesus invites the saved into the kingdom (Mt. 25:34) He will not be inviting people into the church. In places where “kingdom” and “church” are not interchangeable, the word “kingdom” generally has the sense of “rule.” All are “in the kingdom” in the sense that each one is accountable to God for his or her actions (i.e. God reigns or rules over all people). Only those who become Christians are “in the kingdom” in the sense of being a member of the church and thus part of the saved.
More information about the “kingdom” in the sense of the church is available at www.abiblecommentary.com/newtestamentchristianity