I’ve quoted this before, often, but it’s so good it merits re-quotation. From Luther’s 1528 “Confession”:
These are the three Persons and the one God, Who has given Himself to us wholly with all that He is and all that He has. The Father gives Himself to us, with heaven and earth and all created things, that they may be profitable and of service to us. But this gift was obscured and made fruitless by Adam’s fall, and the Son also gave Himself to us, bestowed on us all His works, sufferings, wisdom and righteousness, and reconciled us to the Father, so that, once more alive and righteous, we perceive and possess the Father and His gifts. But such grace would profit no one if it were to remain a hidden secret and could not be imparted to us. So the Holy Ghost also comes and gives Himself completely to us, teaches us the bounty of Christ, makes us perceive and understand it, helps us to receive and keep it, to use it profitably, to administer it and to increase and further its spread among men, and this He does both inwardly and outwardly. Inwardly through faith and other spiritual gifts but outwardly through the Gospel, through Baptism and the Sacrament of the Altar, through which, as through means or instruments He comes to us, applies the sufferings of Christ to us and makes them profitable to salvation.