Ibn Al-Qayyim (may Allah have mercy on him) spoke about monotheism as though it were life itself for the soul. He explained that the heart becomes exhausted and scattered when it clings to people and worldly things, but when it returns to Allah alone, it finds peace and tranquility.
As for “Alone, without partners”, it means complete sincerity, “O Lord, I do not seek people’s praise for my deeds, nor their admiration and I do not place in my heart any rival in your creation of the heavens and earth competing with Your love.”
Then comes, “To Thou belongs the dominion," meaning that everything you fear, hope for or love is already under Allah’s control. People, provision, relief, the future and even your own heart all belong to Allah ﷻ. When a servant truly realizes this, worldly fears become lighter, because he knows that all matters are in Allah’s hands.
“And to Thou belongs all praise," meaning that Allah deserves praise in times of ease and hardship alike, because Allah is All-Wise and Most-Merciful, Entirely Merciful, even when the servant cannot yet understand the wisdom behind events. A believer may cry over something painful, then later discover that Allahﷻ was preparing goodness for him all along.
"And Thou is capable of all things," meaning there is no sin Allahﷻ cannot forgive except shirk (associating partners in worship with Allahﷻ), no worry Thou cannot remove, no broken heart Thou cannot heal, and no distant prayer Thou cannot answer.
The righteous predecessors (salaf al-salih)(may Allah preserve them) would repeat this remembrance often during times of ease and hardship, because it fills the heart with faith, certainty and complete trust in Allahﷻ.
سبحانك اللهم وبحمدك أشهد ان لا اله الا انت استغفرك وأتوب اليك