Question: Why can't I take communion with my loved ones who are Christians from another denomination?

I remember a little tag on a stroller that my wife and I owned that had these instructions on the stroller – “WARNING – do not fold up this stroller while baby is in it!”  We thought the tag was a joke.  I mean how ridiculous is this warning?  Of course, living in a society that is sue-happy, it’s understandable that lawyers from these companies are doing everything they can to prevent companies from being sued for delinquent behavior. 
Sometimes, I think the church gets a similar reputation by putting out all these “Do’s” and “Don’ts” out there, but very few “whys” and so people tend to look at the church as just another warning label that very few people pay attention to.  Maybe that’s why I’m not a huge fan of the small blurb congregations put in their bulletin regarding the doctrinal practice of closed communion.  Can you really teach this practice in a paragraph??? I’m not sure I can teach this in a 1,500-word document, but I’m going try.  Let’s begin with an overview of communion and how others in the world of Christendom practice it.      
There are three prominent views of Holy Communion in the Christian community:
Reform churches – Baptist, non-denominational churches, Assembly of God, and Pentecostal churches believe in a doctrine called Representation – bread and wine represent the body and blood of Jesus and no forgiveness of sins are dispensed through the meal

Transubstantiation – Catholics, Orthodox, and Episcopalians believe that the priest changes the bread and wine into the body and blood of Christ so that there is no more bread and wine when you eat.  They also teach that this meal is sacrificial, rather than sacramental, meaning this: each time you take communion, you are meriting Christ’s forgiveness before God.

The Lutheran Church teaches the doctrine of the Real Presence – We believe from the Bible that four things are present when we receive Holy Communion – bread & wine; body & blood and that Jesus truly dispenses forgiveness of sins through this sacred meal and where there is forgiveness, one can be sure the Holy Spirit is present strengthening and confirming faith in our hearts.   
Lutheran’s adopted the teaching of the Real Presence from Christ himself.  For Matthew writes in his gospel account, Matthew 26:26-29 26… Jesus took bread, gave thanks and broke it, and gave it to his disciples, saying, "Take and eat; this is my body." 27Then he took the cup, gave thanks and offered it to them, saying, "Drink from it, all of you. 28This is my blood of the covenant, which is poured out for many for the forgiveness of sins.
So, the communicant is eating bread that is our Savior’s body and he’s drinking wine, which is his blood.  To what end?  Jesus says, “For the forgiveness of sins.”  Now, the apostle Paul confirms this doctrine of the Real Presence in his letter to the church at Corinth when he states, I Corinthians 10:16 “The cup of blessing which we bless, is it not the communion of the blood of Christ? The bread which we break, is it not the communion of the body of Christ?” (KJV) This is the passage of the Bible where the word, “communion” was adopted by the church – it’s a coming together of both bread and body, wine and blood for the forgiveness of sins.    
Because we are receiving a very personal and intimate meal that was blessed by our Savior, God’s Word instructs us very clearly that we need to know what we are doing while receiving this meal.  Paul, the apostle says in 1 Corinthians 11:27-29 “Therefore, whoever eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of sinning against the body and blood of the Lord.  A man ought to examine himself before he eats of the bread and drinks of the cup.” 
This sets the stage of why the church practices Closed communion.  We Close the table to those deemed too young to understand what is taking place at the table.  But we don’t just close the table to the spiritually immature, we also close the table if mental health deteriorates to such a point in a person’s life that they no longer understand what they are receiving.  In addition to this, the church is also instructed to Close the table to the impenitent or those that have not expressed their sorrow over sin, which makes perfect sense, right?  How can we dispense our Savior’s forgiveness in this blessed meal if a person has openly and defiantly by their lifestyle told God they don’t really care what he instructs for their life because they are going to live their life any old way they want?
But it’s this last scenario that most Christians struggle with, which has to do with our question today, “What about my family member or my good friend, who I know has a living faith in Jesus Christ as I do, but happens to practice their faith in another Christian church?”    
This seems judgmental, it seems elitist on our part, and at least gives the appearance that we are the most unloving people on the face of the earth.  And there’s probably not much I can say that will necessarily change that perception that is out there, but I’m going to try anyway. 
Paul states in the Scriptures:
I Corinthians 10:17 “Because there is one loaf, we, who are many, are one body, for we all partake of the one loaf.”
1 Corinthians 11:26 “For whenever you eat this bread and drink this cup, you proclaim the Lord’s death until he comes.” 
“One body” partaking of “One loaf” reflects the unity that Christians share regarding the Word of God.  But as I mentioned earlier, not all Christians believe the same thing about God’s Word.  So for us to say, “Well, let’s just agree to disagree on what God says about creation, whether the world was created in a billion years or 6,000 years, and set aside our differences…, that does not honor God who clearly tells us in his Word when he created this young earth.  Or for some to say, “I believe that the meal is merely symbolic and not really Christ’s body and blood” or for someone to say, “I believe in infant baptism” while another says, “I don’t believe kids should get baptized till they can make a choice.”  You see, we would be dishonoring God in our worship, if we thought so little of his Word that we ultimately said, “It really doesn’t matter so long as we call ourselves Christians.”  
Paul says, “We are one body,” partaking of “One loaf.” 
And this is where I like to think of communion as “Close” communion.  Certainly, not everyone we commune with has the same exact understanding or even depth of faith as our brothers and sisters communing next to us.  But we do share a common agreement in the faith in that we have all had a basic instruction of God’s Word and we are not obstacles to them by what we teach and they are not obstacles to us by what they believe – but we are partners in gospel ministry who believe relatively the same things about our salvation.
In a religious climate that seems to think so little about God and his Word in some circles, I would like to think that this practice would be refreshing to some, especially those who like us believe that all of what the Bible says is important and vital for our faith.  I’ll end it with our Savior’s words to his very own disciples in John 8:31, “If you hold to my teaching, you are really my disciples.  Then you will know the truth, and the truth will set you free.”