This phrase announces the following good news, which is both healing and a source of happiness:
Man’s spirit and heart, which are connected to most of the creatures in the universe and are almost overwhelmed in misery and confusion on account of this connection, find in the phrase “God is One” a refuge and protector that will deliver them from all the confusion and bewilderment. That is to say, it is as if “God is One” is saying to man:
God is One. Do not wear yourself out having recourse to other things; do not demean yourself and feel indebted to them; do not flatter them and fawn on them and humiliate yourself; do not follow them and make things difficult for yourself; do not fear them and tremble before them; for the Monarch of the universe is One, the key to all things is with Him, the reins of all things are in His hand, everything will be resolved by His command. If you find Him, you will be saved from endless indebtedness, countless fears.
From the 20th word by Master Said Nursi