What does the term "means of grace" mean?

"The Meanies of Grace: Props to the Theological Thugs" explains the term means of grace: "God instituted 'the Ministry of Teaching the Gospel and administering the Sacraments' for this purpose. 'Through [Gospel and Sacraments], as through means, he gives the Holy Spirit who works faith when and where he pleases....' In other words, the Means of Grace are those things through which we receive the benefit of Jesus' suffering and death on our behalf. They are the Gospel Word as proclaimed in the sermon and pronounced in the Absolution, Holy Baptism, and Holy Communion. These establish, grow, and strengthen faith as through them we receive the fulness of the forgiveness of sins, life, and salvation."

Why prayer is not included in the means of grace