Now to the “what” of humility.

Humility (before God) is a proper realization of our sinfulness before God. No degree of pomp, wealth or power can free us from selfishness, covetousness, anger, lust, greed. This is the cognitive realization which is the basis for our humility:

To begin with the first inward humiliation in the mind, in regard of judgment and knowledge, is, when our understandings are convinced, that we are as we are; when we are not high-minded, but when we judge meanly and basely of ourselves, both in regard of our beginning and dependency upon God, having all from him, both life, motion, and being; and also in regard of our end, what we shall be ere long. All glory shall end in the dust, all honour in the grave, and all riches in poverty. And withal, true humiliation is also in regard of spiritual respects, when we judge aright how base and vile we are in regard of our natural corruption, that we are by nature not only guilty of Adam’s sin, but that we have, besides that, wrapt ourselves in a thousand more guilts by our sinful course of life, and that we have nothing of our own, no, not power to do the least good thing.

Humility is not merely an intellectual apprehension, it also includes one affections.

Again, Inward humiliation, besides spiritual conviction, is when there are affections of humiliation. And what be those? Shame, sorrow, fear, and such like penal afflictive affections. For, upon a right conviction of the understanding, the soul comes to be stricken with shame that we are in such a case as we are; especially when we consider God’s goodness to us, and our dealing with him. This will breed shame and abasement, as it did in Daniel.

Sibbes combines these two elements in humility enlisting the fear of God:

The third penal affection is, fear and trembling before God’s judgments and his threatenings, a fear of the majesty of God, whom we have offended, which is able to send us to hell if his mercies were not beyond our deserts. But his mercy it is, that we are not consumed. A fear of this great God is a part of this inward humiliation. So we see what inward humiliation is: first, a conviction of the judgment; and then it proceeds to inward afflictive affections, as grief, shame, fear, which, when upon good ground and fit objects, they are wrought in us by the Holy Ghost, they are parts of inward humiliation.

He then notes as an aside: if we not humble ourselves, we will be humbled by another:

But as for the wicked, they drown themselves in their profaneness, because they would not be ashamed, nor fear, nor grieve for them. But this makes way for terrible shame, sorrow, and fear afterwards; for those that will not shame, grieve, and fear here, shall be ashamed before God and his angels at the day of judgment, and shall be tormented in hell for ever.

Next, Sibbes notes that such knowledge and affection will result in conduct, “It was not a dumb show, but done with his outward expression and his inward affection.” There will be some sorrow, some action or conduct consonant with the affection and knowledge which are the basis for humility.