The Hebrew word kadosh means "set apart".
If the word is repeated twice it describes a more extreme type of being set apart for God (as with the Tabernacle altar) where the object is "contageous" and other objects it touches become normally "set apart". This is normally translated "most holy" or "especially holy".
Except for this issue of contagion, there are not different levels of being set apart for God. However, the manner in which something becomes set apart is part of its history and thus adds a "flavor" of holiness, as described below.
Note that in Orthodox Judaism the word is typically pronounced kodesh.
There are five ways of being set apart for God, four of which can apply to people.
The first way something can become set apart for God is if God simply declares that the thing is special. The first time the word kadosh occurs in scripture is when God sets apart Shabbat as different from the other days of the week (Genesis 2:3). God later sets apart the days of Pesach as different from the other days of the year (Exodus 12:16).
Nothing in the Tabernacle or priesthood was holy simply because God declared it to be holy.
People can be set apart for God in this way. Sometimes this is dramatic, such as the calling to be a prophet, but most people do not experience God asking them to do so many specific things, or to be so isolated from society.
There is no ritual done to things that God declares to be set apart for him. Prophets are called but never anointed.
However, even though we are not all prophets, it is true that God wants us to fit into his plans, and this usually means God has plans for the "big decisions" of our lives such as where to live, what career to have, and if and when to marry. The English word for God choosing these major aspects of our lives is vocation.
Our vocation is not necessarily the work and life we find most pleasing or natural. Moses never claimed to enjoy shepherding the Israelites. Jeremiah wasn't thrilled about being a prophet. Paul was not talented at public speaking. John the Immerser had doubts about the message he was called to proclaim. Jacob wanted fewer wives than were in God's plans, and Solomon wanted more.
People can ignore their original vocation, yet through God's mercy still be part of his plans. (For example, Samson neglected his role as judge over Israel.) But it is wrong to use vocation as an excuse to break vows. God hates divorce and oath breaking. Someone who thinks he or she married or committed to an employer against God's will cannot use the concept of vocation as an excuse to change the situation. God's plans are in some ways flexible, and scripture makes clear that God will work within vows even if those vows were not part of his earlier plans.
Often God only reveals part of a person's vocation to the person. Sometimes all a person is told is, "Be patient. I have plans for you later."
The second way something can become set apart for God is to be physically isolated from the world. Moshe was told that the place with the burning bush (which later scripture makes clear refers to all of Mount Sinai) is holy ground (Exodus 3:5). A curtain was hung up as the final wall of the Tabernacle's innermost room, which became a room so set apart from the world that entering it would kill even the priests.
There is no specific ritual to set something apart physically, but it is necessary to be specific about borders. Much of the meaning of the Jewish prayer shawl is that within its borders is a place set apart for God; some people, at certain points during worship, will even raise the prayer shawl up to be like a tent around their head to emphasize to themselves that in worship they are alone with God.
People can use physical isolation as a way of being holy. Throughout history some of God's people have done a dramatic version of this, living as hermits or monks. More commonly, a temporary isolation helps people to escape from the routines of normal life and focus on God. Scripture is full of "wilderness experiences"; prayer retreats are a modern attempt.
Leviticus 27:28-29 tells us that people can dedicate items to God, and these dedicated items become "especially holy". But people cannot be dedicated, for anything living that is dedicated must be killed. (Thus Samuel's mother, who dedicated him as a baby, was following an idea from her own mind and desperation, contrary to Torah.)
We are not encouraged to dedicate items to God. The Hebrew word translated "dedicated" is in other contexts translated "cursed". Perhaps the best translation is "doomed".
Nevertheless, there are some things that are set apart to God as tools in his hands. Items dedicated to God by his own request are anointed. For example, the furnishings of the Tabernacle were anointed with oil and blood before they became "especially holy" tools of worship.
Are people ever holy in this third way? Kings and priests were: their calling is more than a vocation, for everything they do, each day, must be with God. For kings and priests God has chosen more than the "big decisions". And if they act contrary to God's specific plans it is at best a waste of time, and at worst a disaster for the entire community.
Kings and priests, like the Tabernacle furnishings, were also anointed, since they were tools of God chosen by God.
Items that are "especially holy" can cause holiness to spread by transmission. No ritual is involved.
Whatever touches the Tabernacle's altar become holy (Exodus 29:37). Indeed, this is what altars did--they set things apart for God, so that an animal slaying changed from slaughter to sacrifice.
But holiness does not spread to people by transmission. God made it clear, multiple times, in scripture, that a criminal who grabs hold of the altar gains no safety or benefit. Aharon was set apart by his ritual of anointing, not by the special clothes he wore.
People are never "especially holy". No one can make things set apart for God by touch. But priests and kings can transmit other spiritual characteristics by touch, as in the Tenach's rituals about priests transferring guilt by laying their hands on the heads of animals, or the accounts in the Apostolic Writings of God's Spirit being transmitted to new believers by the laying on of hands. People were healed by touching Yeshua's fringes (Mark 5:30), or by touching Paul's handkerchiefs (Acts 19:12).
Remembering God's commandments makes us holy (Numbers 15:40). Remembering Shabbat keeps it holy (Exodus 20:8).
The Hebrew word for "remember", zachra, means more than thinking about something. Scripturally, to remember is to continue what was once started but has been put "on the back burner". A memorial, zeekaron, is something intended to stir up a memory that reinstates a mood or action that happened long ago. At Pesach the items on the Seder plate should create the same mood as the first Seder. The pile of stones beside the Yarden river would create the same joy and awe as crossing through the river while carrying the ark.
When God remembered Noach (Genesis 8:1), Avraham (Genesis 19:29), Rachel (Genesis 30:22), the Israelites in Egypt (Exodus 2:24) or in battle (Numbers 10:9), Babylon (Revelation 18:5), or a covenant (Genesis 9:15), God was resuming actively carrying out his plans for what he remembered. Remembering Noach meant that God's plans for justice were deemphasized and God's plans for Noach and his family were put in the forefront. Remembering the Israelites in Egypt meant that God's patience for the Amorites had ended, and God's plans for Israel were jump started.
The institution of the Levitical priesthood included memorials. The names of the twelve sons of Israel (an important wording: it is not the names of the twelve tribes, for then Levi would be left out) are engraved on jewels on the High Priest's vest-shoulders and breastplate. Exodus 29:29 tells us that every time the High Priest enters the Tabernacle's tent, these names were "before Adonai" to remind God to act towards the Israelites according to God's plans and Jacob's prophecies--not according to what the Israelites deserved.
We too can set things and people apart for God by remembering them "before Adonai": by asking that God actively make his will for them happen when it seems like God's will is dormant, or by asking for God to live up to covenant promises he once proclaimed. God's people have always done this, and still do so all the time: it's called prayer. Thinking of prayer as remembering things "before Adonai" helps us understand why only prayer that is aligned with God's plans produces results.
Of the five ways to be set apart for God, four can and should apply to all of Yeshua's followers. Just as the Tabernacle's oil and incense each were a blend of four fragrances, our devotion to God should be made up of different flavors of holiness.
Holiness is necessary to see God, according to Hebrews 12:14. It should not surprise us that the flavors of holiness as helping us see God in a different ways.
If we resist our vocation we will not see God "enlarge our boundaries" (1st Chronicles 4:10) as he desires. Yeshua's early followers understood that God calls different people to do different roles in the community, and to receive different spiritual gifts.
If we avoid isolation we will not hear God speak in a "still, small voice" (1st Kings 19:12). Yeshua had a habit of praying by himself in the mornings.
If we shy from our priestly dedication we will not see God "show forth the virtue of him who has called you" (1st Peter 2:9). Yeshua's followers are called priests, and should teach people about God and help God experience people.
If we neglect commemoration of God's plans in prayer, or if we do not "remember from where we have fallen" (Revelation 2:5), then we will seldom see God act in our lives. Yeshua's followers are told to continually pray and intercede so that people can experience God's will in their lives.
Our forefathers understood holiness well, and it has not changed since ancient times.