Say, the Holy Spirit has brought the revelation from thy Lord in Truth, in order to strengthen those who believe, and as a Guide and Glad Tidings to Muslims.
According to most commentators, the Holy Spirit here refers to the
Archangel Gabriel, the angel of revelation (R); see also 2:87c; 2:253; 5:110.
According to al-Rāzī, the abrogation of verses or rulings, mentioned in the
previous verse, was a test for the believers; if they continued to accept the
revelation as coming from God and trusted in His Wisdom, this would make firm
those who believe, in that they would show themselves to be firm in their faith
and the path of their religion.
Nasr, Hossein (2015). Study Quran. http://www.islamicweblibrary.com/wp-content/uploads/2020/04/TheStudyQuran.pdf