Monergism is the stance that God alone works out human salvation without any input from the person being saved. Faith can only save because God first gave the faith to me, and I have no choice but to believe and be saved. This gets past that paradox of whether belief in Christ is actually a work. Martin Luther is considered Monergist, and strongly separated Law and Gospel as sort of necessary opposites.
Monergism is generally in contrast to Synergism, which means that the individual cooperates with God in salvation. Wesley falls more in this category, and he was not willing to separate Law and Gospel as sharply as Luther. Humanity is totally sinful and incapable of properly responding to God, but God gives everyone prevenient grace—a spark of the Holy Spirit allowing us to freely accept or reject the salvation God offers us. God’s grace always goes first, but requires a human response of obedience or rejection.
I threw the Karl Barth quote in there because he was a Reformed theologian who somehow seemed to articulate what Wesley was getting at here.