The Bible says Solomon was the wisest man who had lived at that time, yet even he got swept up into idolatry.
The Bible has much more to say about this issue of Christians marrying non-Christians: To the rest I say this (I, not the Lord): If any brother has a wife who is not a believer and she is willing to live with him, he must not divorce her.
Ye are of your father the devil, and the lusts of your father ye will do.
He was a murderer from the beginning, and abode not in the truth, because there is no truth in him.
God’s ideal for marriage is for Christians to marry other Christians, and raise up Godly offspring in the faith. After a few dates, a Christian will inevitably get to know a person’s beliefs, habits, and things like this.
So even the wise King Solomon made some mistakes in this regard, and it caused him to turn from God.
The Bible (and Jewish tradition) did allow for marriage between a believer and outsider, but only if the outsider converted. Otherwise, they were (and still are) commanded not to marry non-Christians/unbelievers.
It is important to keep in mind that when a believer marries a non-believer, it can lead the Christian astray.
Otherwise your children would be unclean, but as it is, they are holy. A believing man or woman is not bound in such circumstances; God has called us to live in peace.
How do you know, wife, whether you will save your husband?
Or, how do you know, husband, whether you will save your wife?