This is the question that turns many people Catholic. But why? Believe it or not, the fatal word is not "Church," it's "The." But Why? Because as a protestant you frequently answer "What is The Church?" by describing "churches."
For example, some protestants might say "The Church" (singular) is true believers (plural), others will say it includes Roman Catholics, Anglicans, and The Orthodox (plural), still some will say its all who keep Christ's commandments (plural), some say its those (plural) in relationship with Jesus, etc. They are all well meaning, but grammatically wrong.
Why? The question has a definite article, "The," and therefore any answer must too be singular, one.
If one asks, "What is the dog doing in my bed?" it can never be answered by "Dogs are carnivores of the canine family coming in many species..." The first person has asked about a single particular, and the second has responded with describing a plurality of things. So too if one asks "What is The Church?" and another respond "Churches are..." we conclude the first person's question wasn't answered because the second person dodged it. We might do best to re-state the question and politely remind our friend that they haven't answered us at all.
Or if one suggests the whole "church" question is distracting from loving Jesus, what do we do with the following Scriptures?
He is the head of the body, the church (Colossians 1:18)
[Jesus is] the head over all things for the church which is his body (Ephesians 1:22)
If he refuses to listen to them, tell it to the church (Matthew 18:17)
And great fear came upon the whole church (Acts 5:11)
The question then, "What is The Church?" seems legitimate from a Scriptural standpoint. Furthermore, for those asking such questions, trying to steer them away from The Scriptures will only seem, and perhaps is, dishonest. There are real people with real questions that need real answers, not evasion.
The Nicene Creed as early as 325 A.D. reflects the Scriptural truth of "The Church" as both one and whole. It is recited by Catholics, Anglicans, Methodists, Presbyterians, many Congregationalists, and even some Baptist churches. This means when people of those traditions talk about "The Faith," they're describe it using The Creed. When their believers speak of "my faith" it is assumed it conforms to this universal form of faith.
For our Evangelical and Non-Denominational brethren there are rarely any universal declarations of what they believe as a group. Individual faith leaves wiggle room for variance or contradiction between believers about who God is, what The Church is, etc. However, if you privately ask their pastors what they believe and preach, most will say it conforms to The Nicene Creed. And those at The Nicene Council were Catholic Bishops. Anyhow, The Creed states:
I believe in one holy catholic and apostolic church.
This is how The Catholic Church tries to answer the question, "What is The Church?" Furthermore, The Catholic Church renewed several expressions that describe "The Church" at Vatican II. We find that each comes from The Holy Scriptures. Each description matches one of the Persons of The Holy Trinity: The Father, The Son, & The Holy Ghost.
The Church is The People of God [The Father]
The Church is The Body of Christ
The Church is The Temple of the Holy Ghost
You'll notice to answer "What is The Church?" the possible answers are not "Peoples" but People, nor "Bodies" but Body, and likewise not "Temples" but Temple. An answer in the singular, for a question put forth in the singular.
So "What is The Church?" We'll go into "The People of God" next week. What is, and what it ain't.
[The mosaic above is featured at The Chancery of the Ordinariate of the Chair of St. Peter in Houston, TX. It depicts St. Augustine holding "The Church" depicted signified by a church building.]