[24a bottom] The Gemarah discusses the principle of impurity through one’s hands. R’ Rosner: This rule is applied nowadays through the laws of washing our hands before bread. Anytime there is Hesach Hadaas (an interruption of focus), one would need to wash them again.
E’s Lesson: We should always be focussed on what we are doing and not get distracted. Especially when we are involved in learning and doing Mitzvos, we should always give our task 100% of our mind and efforts.