Rabbi Yaakov says:
One who walks on the road while reviewing a Torah lesson and interrupts his review to exclaim: “How beautiful is this tree!” “How beautiful is this plowed field!” – Scripture considers it as if he bears guilt for his soul.
Does this sound harsh or what?!!!
But it is intended to drive home the important of focusing on the task at hand – particularly when the task at hand is the study of Torah / Scripture.
If we are easily distracted we will never learn. If we are easily distracted, when we get to less interesting material we will never learn it.
In addition – the commentaries by other rabbis note that, in that day and time, great dangers lurked on the roads. Bandits and robbers abounded. The rabbi believed that being engaged in the study of Torah / scripture put one under the protection of the LORD. Obviously – to stop one’s study in such a situation was to put oneself in danger!
Christians might connect this point about danger on the roads with a parable of Jesus – the Good Samaritan who cared for a man attacked by robbers and left for dead on the road to Jericho.
This is not to suggest that noticing the beauty of the world around us is a bad thing! There is simply, in the mind of the rabbi, a time and a place for that – perhaps when our studies are over and we are headed home in the company of our friends or loved ones.