Sforno on Numbers 9:7/ספורנו על במדבר ט׳:ז׳

1אנחנו טמאים לנפש אדם למה נגרע, seeing that the ritual impurity we have incurred was incurred in the process of our fulfilling a positive commandment, why should the result of this be the misdemeanour of not fulfilling such an important commandment as observing the Passover at the appointed time?

2במועדו, seeing that this is a commandment which can only be fulfilled at its appointed date?