Seeing it is the proper office of the Holy Spirit to seal the promises of God in our hearts, how do you attribute this to the sacraments?

There is a great difference between the one and the other. The Spirit of God in very truth is the only One who can touch and move our hearts, enlighten our minds, and assure our consciences; so that all this ought to be judged as His own work, that praise may be ascribed to Him alone. Nevertheless, the Lord Himself makes use of the sacraments as inferior instruments according as it seems good to Him, without in any way detracting from the power of the Holy Spirit.