The way you become holy, Ramchal offers very near the end of this chapter and of the entire work, “is with a lot of abstention, with serious reflection upon the mysteries of G-d’s great involvement in the world and upon the secrets of creation, and with the sure knowledge of G-d’s exaltedness and praise”.
For, “only then will you have become attached to Him strongly and know how to concentrate your thoughts while moving about in the world and making use of it” in holy ways. Indeed, “without all this it‘s impossible to reach this great height. You’d remain corporeal and of-the-earth like all other people” rather than be holy.
What also helps, he goes on to say, “is a lot of solitary meditation, and abstinence” so that “your soul can more easily strengthen and attach itself to G-d”, given that what most especially detracts from this trait is “a lack of knowledge of the truth, and the over-association with others”.
Once you attain holiness, Ramchal offers, “you can grow to an even higher level, termed ‘Holy Inspiration’, where your intellect will rise above all human capabilities. That will allow you to enjoy a yet higher form of attachment to G-d” that is far beyond our ken.
Attain that, and “the keys to the Resurrection of the Dead will be passed on to you as they were passed on to (the prophets) Elijah and Elisha”. Your having attained that “would indicate the great degree of attachment to G-d you’d have come to experience”.