What does the term “Pure Joy” mean? Does this connote that the Joy is undiluted with sadness or other negativity, or does this connote that the intention is pure.

The Gemara on amud aleph quotes the verse about rejoicing on Yom Tov (Devarim 16:15): 

שִׁבְעַ֣ת יָמִ֗ים תָּחֹג֙ לַיהוָ֣ה אֱלֹהֶ֔יךָ בַּמָּק֖וֹם אֲשֶׁר־יִבְחַ֣ר יְהוָ֑ה כִּ֣י יְבָרֶכְךָ֞ יְהוָ֣ה אֱלֹהֶ֗יךָ בְּכֹ֤ל תְּבוּאָֽתְךָ֙ וּבְכֹל֙ מַעֲשֵׂ֣ה יָדֶ֔יךָ וְהָיִ֖יתָ אַ֥ךְ שָׂמֵֽחַ׃

You shall hold a festival for the LORD your God seven days, in the place that the LORD will choose; for the LORD your God will bless all your crops and all your undertakings, and you shall have nothing but joy.

Rashi notes that the phrase “ach sameyach”, nothing but joy, comes to teach that there also is a mitzvah of rejoicing on Shemini Atzereth.  Some of the commentators (see Rabbenu Bechaye) question, is it not  a general rule that “ach” is a limiter and usually teaches a limit or restriction, not an inclusion. Some answer that the verse is alluding to a limitation within the inclusion, that being while rejoicing, there still should be some internal self-constraint on the Joy.

According to that interpretation, the phrase “nothing but joy” or “pure joy”, means Joy l’shem shamayim and not for personal gratification.  I would like to suggest a different angle.  Namely that pure joy or nothing but joy is referring to allow for happiness without pessimism, fear or negativity.  I often tell my clients, especially couples, “It takes a lot of mesiras nefesh to have fun”.

I mean it.  There are compelling, destructive psychological urges to downgrade positive and happy experiences by complaining, being pessimistic or harping on minor disappointments within an overall good experience.  Yet, it is healthy to be positive, optimistic and allow yourself, especially in a relationship to enjoy a good time.  Do not let your fears and sense of unworthiness to sabotage moments of goodness in your life.