The Rebbe reassures the writer to trust fully in Hashem’s guidance and not waste energy on worry. Since the Rebbe Rayatz already gave him a blessing, it will certainly be fulfilled. He encourages choosing confidence and joy over anxiety, as problems will be resolved with Hashem’s help. He ends with blessings for a joyful and kosher Pesach.
https://www.torahrecordings.com/rebbe/004_igros_kodesh/nissan/984