To say "No" is easier than to say "Yes".
Even without opening or stretching the mouth too much, the "No" comes out loud enough.
Saying Yes takes some effort on the lips and the muscles around the mouth.
Similarly, to obey is more difficult than to disobey.
To obey is to submit ourselves to orders and instructions, even though those orders and instructions are for our good.
But somehow our first reaction will be to say "No" and we just don't want to submit because we tend to treasure our freedom more.
Even when those orders and instructions come from God, that does not quite change our attitude.
Hence in the 1st reading, God says this to His people:
If you are willing to obey, you shall eat the good things of the earth.
But if you persist in rebellion, the sword shall eat you instead.
So we already know what is good for us. It is now up to us to make our decision.
May we submit to the Commandments and instructions of the Lord, for the Lord only wants everything for our good.