is,

Firmness; solidity or toughness; power or vigor of any kind; power of resisting attacks; power of mind; intellectual force.

And Jesus answered him, The first of all the commandments is, Hear, O Israel; The Lord our God is one Lord: And thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind, and with all thy strength: this is the first commandment. And the second is like, namely this, Thou shalt love thy neighbour as thyself. There is none other commandment greater than these.
Mark 12:29-31