Rashi comments on the verse, “Today God your Lord commands you to obey these laws” (Deut. 26:16), saying, “Each day they should be in your sight like something new, as though you had received these commands on that very day.”
The suggestion that our sages offer – to treat old mitzvot as if they are new and exciting – only seems to accentuate the problem.
New tasks are relatively easy to muster excitement for.
When it is only as though they were new – that is much more difficult.
According to the Midrash (Ecclesiastes Rabba 1:13), we should thank God for creating us with the attribute of forgetfulness, for as a result we can learn things more than once.
If we were unable to forget, then whenever we would study some subject a second time, the experience would be identical to the first time.
Now, thanks to forgetfulness, our learning always contains an aspect of renewal.
–Rabbi Adin Steinsaltz