Inertia  n. – a physical characteristic of all matter to preserve its state of uniform motion unless acted upon by an external force.

The more massive the body, the more force is required to make it change its direction.  This is true of physical bodies; it is true of spiritual ones.

This week’s Bible Study illustrated that, both in ancient times and in our day.

(bt chap. 23 p. 182 par. 6 “Hear My Defense”)
6 The elders then revealed to Paul that there was a problem in Judea that involved him personally. They said: “You behold, brother, how many thousands of believers there are among the Jews; and they are all zealous for the Law. But they have heard it rumored about you that you have been teaching all the Jews among the nations an apostasy from Moses, telling them neither to circumcise their children nor to walk in the solemn customs.”—Acts 21:20b, 21.

This involved not only the Christians in general in the city, but the older men who made up the then-governing body of Jehovah’s people.  Some of these men wrote parts of the inspired word of God.  Many of them would have known Jesus personally.  They had witnessed miracles.  Still, they clung to what was now abandoned by God.  Jehovah tolerated that inertia, knowing our weaknesses and limitations.

Do we suffer from it today?  Inertia is a physical characteristic of all matter, and it is safe to say that it is a metaphysical characteristic of all grey matter.

I think there is a small piece of evidence to support that in the question for paragraphs 7 and 8: “(b) Why did the mistaken thinking of some Jewish Christians not amount to apostasy?”

“Some”?   The Bible clearly states that this view as shared by all.  That would include the older men, which is evidenced by their ill-fated attempt to appease the Jews by putting Paul through a purification ceremony.  They also indicated that the ruling of Acts. 15:29 applied to the Gentile Christians only. (Acts. 20:25)

Why  would we say “some” when the Bible says “all”.  Is it because our modern-day mental inertia will not countenance the thought that the governing body—ancient or present—could be so wrong about something?