When Martin Luther wanted to he could succinctly state the centrality of the Gospel and faith in God’s grace.  In 1522 he wrote to Hans von Rechenberg:

This is the noblest and dearest virtue of faith, that it closes its eyes and simply and joyfully leaves everything in the hands of God.  It does not desire to know why God acts as He does, and it still holds Him to be the Highest Goodness and Justice, although to all reason, the senses and experience, nothing appears but wrath and injustice.  That is why faith is called the proving of things not seen, and even the very opposite to what is seen.  Therefore, this is the highest honor and love towards God and the highest degree of such honor and love, that in these contrary things you can regard and praise Him as good and just.  Here the natural eye must be completely plucked out, and there must be nothing but sheer faith.  Otherwise there will be a grim and fearful vexation of spirit.