Let us not therefore enquire into these things. For as the devil fell by pride, so he who is wrought upon by him is anointed unto pride. Wherefore, I beseech you, let us all be earnest to be far removed from this affection, that we may not fall into his condemnation, that we may not subject ourselves to the same punishment, that we may not partake of the vengeance. He who is puffed up therefore, suffers the same punishment with the devil. For the beginning of pride is not to know the Lord.
Pride is the beginning of sin, the first impulse and movement toward evil.
Perhaps indeed it is both the root and the foundation. As if one should say, the beginning of chastity is to abstain from the sight of an improper object, that is the first impulse. But if we should say, the beginning of chastity is fasting, that is the foundation and establishment. So also pride is the beginning of sin. For every sin begins from it, and is maintained by it.