When something is declared as "truth" in the Bible it means it comes from the Lord and is true down to the deepest levels of reality.

1094. 'A slave of slaves will he be to his brothers' means the lowest thing in the Church. This is clear from the nature of external worship separated from internal. That external worship regarded in itself is nothing at all unless internal worship exists to sanctify it may become clear to anyone. What is external adoration without adoration of the heart but a mere gesture of the body? What is prayer on the lips if the mind is not in it but a meaningless babble? And what is any activity if there is no intention within it but a kind of nothing? Consequently everything external is in itself something soulless, living solely from that which is internal.

[2] The character of external worship separated from internal has been made clear to me from many experiences in the next life. The sorceresses and witches there attended church and the sacraments during their lifetime as frequently as any others did. The deceitful likewise, indeed more often than others; and so also those who delighted in robbery, as well as the avaricious. Yet they are in hell where they utterly hate the Lord and the neighbour intensely. With them internal worship had been present in the external either to the intent that the world might see it, or so that they might gain possession of the worldly, earthly, and bodily things they coveted, or so that they might mislead by an outward show of holiness. Or it may have been out of an acquired habit. That such people are very prone to worshipping whichever god or idol favours them and their own evil desires is quite clear. This is especially clear from the Jews who, because they made worship consist in nothing except external things, fell away so many times into idolatry. The reason is that such worship in itself is altogether idolatrous, for they are worshipping what is external.

[3] The external worship of the nations in the land of Canaan, who worshipped the baals and other gods, was very similar. They had not only temples and altars but also sacrifices, so that their external worship differed little from the worship of the Jews. The only difference was that the name they had for their god was Baal, Ashtaroth, or some other, whereas the Jews had the name Jehovah. As they also do even today, the Jews imagined that merely the naming of Jehovah made them holy and chosen people, when in fact that led rather to greater condemnation of them than of others. For that naming made them capable of profaning what was holy, which the gentiles could not do. Such is the worship called 'Canaan', who is referred to as 'a slave of slaves'. That 'a slave of slaves' means the lowest thing in the Church may be seen in the next verse.