Everything that leads to faith, to openness to God, is required. All the other acts which are not directly tied to faith operative in love are left by Christ to human liberty, of the individual and of those who are leaders in the Church. Religious experience may oblige us that we fast and participate in religious practices. This depends on the prudence and wisdom of those in charge. This shouldn't be done in a stifling way.
Individuals decide how to be creative in their virtues.
One may express love of God by loving in the family, another in serving the poor. There are no set limits about what to do. The leaders of the Church decide what is to be left for individuals and what all should do. Saint Thomas then describes whether the New law requires external and internal acts. In the latter question he brings in the sermon on the Mount.