According this this page, Roman Catholics, Greek Orthodox, American Evangelicals, and Non-denominational Churches hold to the belief that humans have the ability to accept the gospel pre-conversion at some capacity. The gospel thus becomes a work, and not a gift. You hear language like this sometimes: “If you want to receive forgiveness then you must pray the sinners prayer or accept Jesus into your heart, etc." This is synergism. The Lutherans and the Reformed hold to the belief that humans cannot by their own reason, will, or strength come to the knowledge of Salvation, but that the Holy Spirit through the Word enlightened them and converted them. In other words, the human will is the object, not the instrument of conversion. This is monergism: God is the one who makes a Christian and sustains the Christian. These two different beliefs have huge implications on justification, but also sanctification.