The Work Of God is Faith.

Christ's answer was plain enough: This is the work of God that ye believe. Note, The work of faith is the work of God. They enquire after the works of God (in the plural number), being careful about many things; but Christ directs them to one work, which includes all, the one thing needful: that you believe, which supersedes all the works of the ceremonial law; the work which is necessary to the acceptance of all the other works, and which produces them, for without faith you cannot please God. It is God's work, for it is of his working in us, it subjects the soul to his working on us, and quickens the soul in working for him, that faith is the work of God which closes with Christ, and relies upon him. It is to believe on him as one whom God hath sent, as God's commissioner in the great affair of peace between God and man, and as such to rest upon him, and resign ourselves to him. - Matthew Henry