What is the meaning of the Hadith: "Recite the Qur'an as long as your hearts are united upon it, and if you differ, then stand up from it," and is what the questioner does, reading the Qur'an quickly to make up for what he missed, fearing a decrease in faith, correct?

The eagerness to recite the Holy Quran is one of Allah Almighty's blessings upon His servant, and it is among the best acts of worship. The righteous predecessors used to regularly maintain their daily recitations. Therefore, for whoever does not find time for contemplation, there is no harm in reading quickly.

As for the Hadith: "Recite the Quran as long as your hearts are united. If you differ, then stand up from it"; what is meant by it is the discord and contention of hearts due to a poor understanding of religion or ignorance of the established recitations. One must abandon reading that leads to schism and division. It does not mean abandoning the recitation of the Quran in general; rather, the Hadith aims to preserve the unity and harmony of Muslims.