How can a Muslim be among the righteous servants of God and live a happy, tranquil, and peaceful life, and does this require a complete knowledge of the Islamic sciences?

A person becomes righteous by performing their obligations, avoiding prohibitions, and striving in supererogatory acts and matters that are disliked. Whenever they err, they hasten to repent, seek forgiveness, and perform good deeds. They seek assistance in this through prayer, the companionship of the righteous, seeking knowledge, and contemplating Allah's names and attributes and the Last Day. A good life is attained through righteous deeds, "Whoever does righteousness, whether male or female, while he is a believer - We will surely cause him to live a good life," which is the life of the heart and its bliss through faith and the knowledge of Allah, and it is experienced in this world, in the Barzakh (definition) (interim period after death), and in the Hereafter. As for a life of hardship, it is for those who turn away from the remembrance of Allah.