Complex sentence: Psalm 100 is omitted on Shabbat and Yom Tov because the Thanksgiving offering was not offered on these days in the Temple only communal offerings were brought on these days.
Split into simpler sentences: Psalm 100 is omitted on Shabbat and Yom Tov because the Thanksgiving offering was not offered on these days in the Temple. Only communal offerings were brought on these days.