One of the most commonly attempted arguments against polygamy makes the assertion that polygamy is supposedly not the "original plan of God for marriage". This assertion is based solely upon two sequential factors.

1. Jesus's reference to "at the beginning" in Verse 4 of the Matthew 19:3-9 passage, and thus,
   
   
2. the "Beginning" story: Adam and Eve.

That "at the beginning" phrase, which Jesus used there, of course, was only addressing divorce, not polygamy.

Moreover, there is an additional very exegetically important matter to note about all this. Namely, the very story of "the beginning" (with Adam and Eve) ---indeed, the entire book of Genesis (which starts with the first three words, "In the beginning")--- was written by Moses. And Moses was a polygamist with two wives! Certainly, the very mortal author of the story "at the beginning" would know what he wrote and whether his own polygamy was not part of "God's plan" (if it was not)!

Accordingly, it is clear that that phrase, "at the beginning", is simply not relevant to the topic of polygamy, anyway.

Nevertheless, though, that phrase is what forms the basis for the subsequent factor pertaining to Adam and Eve.

Namely, the argument asserts that, because the Scriptures only record that God seemingly only made "one Eve" for Adam, that somehow implies an "original plan of God for marriage" only for monogamy. The resulting implied speculation from that is that polygamy is to be perceived as somehow against that perceived "original plan of God for marriage".

Upon deeper investigation, however, that speculative assertion does not hold up.

If doctrine would hold people to a perceived "original plan of God", then at least two things must also be binding upon mankind. For examples,

1. people must only walk around in nudity, and
   
   
2. people must never die.

Of course, to suggest such things is an absolute absurdity.

According to the Bible, the reason that those two examples are obviously not binding as doctrine is because of Adam's sin. That sin of Adam had forever after changed (as it were) the "plan of God" as applies to us for doctrine.

The Scriptures inform us that "the wages of sin is death" (Romans 6:23). From that, the Bible further explains that, "Wherefore, as by one man [[ i.e., Adam ]] sin entered the world, and death [[ entered the world ]] by sin; and so death passed upon all men, for that all have sinned." (Romans 5:12.)

When Adam sinned, death entered in.

Adam's sin is why we now die. And it is also why we now wear clothes rather than remaining nude, according to Genesis 3:21.

The fact that we now wear clothes and do die is the proof that we are no longer under any perceived "original plan".

So what has God planned for us instead? He gave us "the second Adam", which is Christ, that we might have life everlasting in Him (per John 3:16.).

"And so it is written,
The first man Adam was made a living soul;
the last Adam [[ which is Christ ]] was made a quickening spirit."
1 Corinthians 15:45.

The first Adam brought death by his sin. The second Adam, which is Christ, brought life by His righteousness.

"Howbeit that was not first which is spiritual,
but that which is natural;
and afterward that which is spiritual.
The first man is of the earth, earthy:
the second man is the Lord from heaven.
1 Corinthians 15:46-47.

Adam was of the flesh, while Christ is of the Spirit.

Because Romans 8:1 shows us that we are to walk in the Spirit and not according to the flesh, we are certainly NOT supposed to follow after the example of the first Adam (who was of the flesh), but after the second Adam (who is of the Spirit), which is Christ.

With this now realized that we follow after the "second Adam", Christ, we look to Christ as the example set for us in the true and current "plan of God for marriage". And this is explicitly confirmed and explained for us in Ephesians 5:22-25.

"Wives, submit yourselves unto your own husbands, as unto the Lord. For the husband is the head of the wife, even as Christ is the head of the church: and he is the saviour of the body. Therefore as the church is subject unto Christ, so let the wives be to their own husbands in every thing. Husbands, love your wives, even as Christ also loved the church, and gave himself for it".
Ephesians 5:22-25

This is very explicit. The "plan of God for marriage" is detailed as being modeled after, not the example of the first Adam (of flesh) and his wife Eve, but after the example of the second Adam, which is Christ (of Spirit) and His Churches.

Following this model, each husband is to love his wives as selflessly, "footwashingly", and life-givingly as Christ so loves the Churches (that He laid down His life in the depth of such love). So too, each wife is to love her husband as each Church so loves the one and only Christ Jesus.

As there is only one Christ for the Churches, there is only one husband. And as there are more than only one Church loved by Christ, it would not be sinful if there be more than one wife, of course.

This is confirmed, of course, by the Parable of the Ten Virgins in Matthew 25:1-13. The Lord Jesus Christ described Himself as the polygamist Bridegroom for the "five wise virgins", which are the Churches.

So, in conclusion, what we see is that the "plan of God for marriage" is very explicitly NOT after the model of the fleshly, death-causing first Adam and his (Scripture-recorded) apparent "one" wife, Eve.

Rather, the Bible is clear that the current "plan of God for marriage" is after the model of the Spiritual, life-bringing second Adam, Christ, and His Churches.

Also See:

   Remember Moses wrote it ©

For a much deeper analysis of these above points and much more, see:
   "Question of God's Original Plan for Marriage?",
  [a 14-part Analysis at TruthBearer.org]