A "600 monk" (or simply a "600") is a type of invincimonk who can have more than 55 HP. It is a common misconception that they need 600 or more health, but in reality they can work with nearly any amount. As with most invincimonks, this type of build is mostly used for farming. 600 monks make use of the skill Spirit Bond to stay alive. For this reason, they are sometimes called Spirit Bonders.
The general purpose of a 600 monk is farming for loot. Using Smiting Prayers to deal damage, the player can stay alive by using Protection Prayers Enchantments. These enchantments are commonly activation on hit, which means that the enchantments only activate when attacked. For self-healing and preservation, the only necessary skills are Protective Spirit and Spirit Bond.
Using just two skills is ill-advised, even though it can be done. There are plenty of other skills that can aid in farming and make it more productive. Shield of Absorption, which was updated on 2006 October updates, is a common supplemental skill. During this update Spirit Bond was changed so it would only trigger the healing ten times instead of the enchantment wearing off. Shield of Absorption allows for many enemies to be aggroed at once, while with Spirit Bond alone, only fighting 8 to 5 creatures is possible, depending on whether the player is in hard mode or not.
To maintain energy it is recommended to use either Essence Bond or Balthazar's Spirit. This way every time the player is hit, he will also gain energy, thus never running out. To make these enchantments last longer, one may want to equip Blessed Aura. If Life Attunement is mixed with Spirit Bond the player will be healed for more and if Spell Breaker is added, enchantments will be guaranteed to last their duration while Spell Breaker is in effect. One thing to remember is that interrupting spells and attack skills are the number one cause of death for 600 monks. To prevent this, add Mantra of Resolve or use Spell Breaker to counter spell interruptions.
Keeping alive is one thing, but damage must also be dealt to your foes if you want the loot. This is where spells like Retribution come in, causing enemies that attack to take in damage. Something else that can be used is Holy Wrath which combined with Retribution can really do serious harm to your attackers.
Assistance may be needed due to the effects that Holy Wrath can cause such as loss of energy. It's also helpful if a team-mate has some of the same skills and enchantments so that once energy reserves run low, they can offer support.
Below is an example of what an effective skill set might look like for a 600.