1 Kings 19:19-21 / Matthew 5:33-37
If we know something about computer language, then we will know that at its very basics, it is about "1" and "0".
Putting it simply in understandable language, it is about "Yes" or "No". How this works can be seen in a flow-chart where the flow goes from one "Yes" to the next "Yes". If there is a "No" then it goes to another flow process.
But we don't usually talk in that kind of way. We will say things like "Yes, but.. maybe" or "Yes, if ..."
In other words, our "Yes" is not always a committed and convicted "Yes". The same can be said of our "No"
Elisha, in the 1st reading, also had the same problem. When Elijah passed near to him and threw his cloak over him, Elijah was calling him to follow him.
He ran after Elijah and said "Yes" and then came the "ifs, buts and maybes. A simple question from Elijah was all it took to clear up Elisha's mind and with that he also gave up his oxen and plough.
Seeing all that go up in smoke was certainly not easy but the "Yes" that was required demanded nothing less.
Jesus also emphasized that when He said this: "Yes" if you mean yes, "No" if you mean no.
Putting it simply, let we say "Yes" to Jesus and "No" to the devil, and mean it. Anything more than this comes from the evil one.