......Adultery.

Firstly, I love my wife and hove no idea what that beautiful woman sees in me, but I am glad she does. I have never been unfaithful to her nor do I want to be.

I speak about this from a POV of wanting to be stronger when asked this question from a non-believer.

I try to consider the arguments from their side in referencing polygamy and concubines of very prominent figures in the Bible.

There are some other arguments I have to suggest, BIBLICALLY, that polygamy was not so much condoned as it simply was not punished or seen as adultery.

So taking that route, I see adultery as a married man having or wanting to have sex with another man's wife. I am looking at this purely BIBLICALLY.

It is a difficult subject to broach and has many different opinions. However, my opinion is adultery is a married person having sex with a married or unmarried person.

I also see polygamy as not only wrong but a sign of madness.

Keep this civil and Biblical please. In trying to have an honest discussion, graphics will only kill the discussion.

There are lots of tangents and rabbit holes so please resist and stick to the subject at hand. Do not reference any specific acts.

So, Biblically, what is adultery?

1 Timothy 3:2

Ok , I got 5 min then can't comment again til late tonight.

If I happen to look somewhere and accidentally see a beautiful woman then I have to stop that image cold right there before it gets to my mind then to my heart where it can become lust. If I lust in my heart then I have done it. And no its still not too late to repent, thinking I'm already guilty and going ahead will only lead to maybe cover up or even murder !

I compare the societal acceptance of plural marriage to that of slavery.

God has an ideal set before us from the beginning of time with Adam and Eve yet through the ages of the patriarchs we had both plurality of marriage and slavery. But even then adultery was clearly defined as sexual relations outside of a covenant relationship between man and wife. Likewise there were clearly defined rules for slavery as well. Ultimately with God's ideal set before us in the Year of Jubilee.

So God's ideal, one man one woman for life. No slavery.

Man is flawed and has in years past and present codified practices far from ideal.

God works from within and today society has by and large moved towards His ideals in socially acceptable practice if not in fact.

Adultery - Voluntary sexual intercourse by a married man or woman with someone other than his or her mate.

Polygamy was permitted but still wasn't what God intended. When God chose the Israelites as his people, polygamy already existed among them, although it apparently was far more common to have just one wife. God did not require families to break up where there was more than one wife. Instead, he strictly regulated the practice
So, with the start of Christianity God restated that it was not proper and would no longer be without punishment.

The word fornication is all inclusive. Fornication from the Greek por·neiʹa, a term used in the Scriptures to refer to certain sexual activities forbidden by God. It includes adultery, prostitution, sexual relations between unmarried individuals, homosexuality, and bestiality

When Jesus Christ was on the earth, he restated this position in answer to those who asked about divorce and remarriage. He said: “Did you not read that he who created them from the beginning made them male and female and said, ‘For this reason a man will leave his father and his mother and will stick to his wife, and the two will be one flesh’? So that they are no longer two, but one flesh.” Jesus added: “Whoever divorces his wife, except on the ground of fornication, and marries another commits adultery.” (Matthew 19:4-6, 9) From this it is obvious that taking one or more additional wives is also adultery

That this toleration of polygamy was only temporary can be seen not only by what Jesus stated regarding God's original standard for marriage but also by what the apostle Paul wrote under the inspiration of God’s holy spirit. He said: “Let each man have his own wife and each woman have her own husband.” (1 Corinthians 7:2)

if you marry a divorced person you are commmmiting adulteryif youconsort with idols

Yes, David committed adultery. Since the case involved David, with whom God had made the Kingdom covenant, God chose to make an exception and deal with the matter himself.

David and Bath-sheba were not to escape all consequences of their sin. “Because you have unquestionably treated God with disrespect by this thing,” Nathan told David, “also the son himself, just born to you, will positively die.” Their child grew sick and died.

Agreed David was an adulterer with Bath-sheba. I will step out there and also offend many on here - marriage is a covenant between man and woman. Divorce and remarriage while the first spouse is still alive is adultery. Biblically. Yes, there are tons and tons of folks in churches today that according to the Bible are adulterers who are "remarried". It is not my battle to fight or argue. Its very clear in the Bible.

1st Timothy 3:2 Is a good example.
A pastor is representative of Jesus, the good Shepherd. And the church his flock also represents the bride of Christ. If a pastor is a false teacher or conforms himself to worldly thing, then this would be c onsidered adultery, biblically. In both the old testament and new testament when followers of God turn from God. This is considered adultery. Plural marriage was never God's plan. Abram had Hager because he hearkened unto Sarai.
Jacob's Plural marriages were a result of Labans deceiving him in to marriage with Leah rather than Rachel.
But there was only the law on a man's heart. This is why Israel was Chasen to pave the way with the written law to Abraham's seed Jesus Christ so we could have redemption through Him fulfilling the law.
One man, one Woman has always been God's plan. One Redemer one bride. Has always been God's plan.
For we are saved by the grace of God Though faith in the perfect work of our redeemer Christ Jesus.

Lust.

"God's plan"?
How would any man know of God's plan?

Infidelity in the marriage, including the church marriage to Christ.

James 4:3-4

3 When you ask, you do not receive, because you ask with wrong motives, that you may spend what you get on your pleasures.
4 You adulterous people, don’t you know that friendship with the world means enmity against God? Therefore, anyone who chooses to be a friend of the world becomes an enemy of God.

Bowhunter
To become as God's or to desire to is adultery against God.

When Eave and then Adom both took of the fruit they sinned.
For the wages of sin is death.

If you don't think David and Solomon were punished for having multiple wives, you should look at how messed up their families were. This was a direct result of having more than one wife.

If we don't think Abraham kinda messed up by not taking Gods' promise, seriously take a look at how that turned out in today's stage, and Sarah was ok with it.

Bingo.
And look at Jacob's mess of a family.