The origins of this saying are quite strange. During the depression when everything was scarce, people will fill up a fresh tub of water to bathe in and then each family member would wash. As each person used the bath, the water became more and more murky. By the time it came to wash the baby, you’d have to be careful not to loose the baby in the bathwater when you threw it out.
Now the history is quite strange but the saying is now used for something more profound. When you are tossing out the waste of something, be careful not to throw out something valuable in the process.
It’s THAT meaning I’m using here, when it comes to reading the gospels.
You see, in one of the gospel accounts of Jesus’ resurrection, there is text that doesn’t quite match, doesn’t quite fit… in fact, in most Bibles, there’s even a note that this text was NOT in the original manuscripts or other matching texts.
The part of the Gospel of Mark that is obviously written by Mark ends with Mark 16:8. The remaining verses (9-20) have a different style and structure than anything Mark had written. Some people believe that Mark actually ended at verse 8 while others believe a page was lost before printing and another follower of Mark then added this remaining text more from his own memory of what Mark discussed.
In either case, most scholars agree that these verses are not actually from Mark (hence the disclaimer in our bibles today).
Now, some people seeking to disprove the gospel as a whole, point to this set of verses as reason to doubt the whole thing. Even though the rest of the scripture has an immense about of supporting documentation, even though 11 of the apostles and dozens of other disciples went to extremely brutal deaths holding strong to the truth of these events, some people will take these 12 verses as a reason to toss the whole thing.
Still other groups have chosen to grab these verses as foundational to their beliefs. Assembly of God has taken these verses as vital to their practices, specifically 17-18 “And these signs will accompany those who believe: in my name they will cast out demons; they will speak in new tongues; they will pick up serpents with their hands; and if they drink any deadly poison, it will not hurt them; they will lay their hands on the sick, and they will recover.”
They believe that if you don’t display these signs, you don’t believe.
So the important thing to remember is that there is no other body of works in the world with as much supporting documentation as the bible. In those rare cases where they place a disclaimer on the text, it’s because the support for that text does not measure up to the support of the other texts. Don’t gloss over those disclaimers and don’t throw the whole gospel out when you toss these variant scriptures.