As Lutherans, we are all familiar with Luther’s seal, but may not necessarily know or remember what the symbols represent. Hear from Luther himself:
There is first to be a cross, black [and placed] in a heart, which should be of its natural color, so that I myself would be reminded that faith in the Crucified saved us. For if one believes from the heart he will be justified. Even though it is a black cross, [which] mortifies and [which] also should hurt us, yet it leaves the heart in its [natural] color [and] does not ruin nature; that is, [the cross] does not kill but keeps [man] alive. For the just man lives by faith, but by faith in the Crucified One. Such a heart is to be in the midst of a white rose, to symbolize that faith gives joy, comfort, and peace; in a word it places the believer in a white joyful rose; for [this faith] does not give peace and joy as the world gives and, therefore, the rose is to be white and not red, for white is the color of the spirits and of all the angels. Such a rose is to be in a sky-blue field, [symbolizing] that such joy in the Spirit and in faith is a beginning of the future heavenly joy; it is already a part [of faith], and is grasped through hope, even though not yet manifest. And around this field is a gold ring, [symbolizing] that in heaven such blessedness lasts forever and has no end, and in addition is precious beyond all joy and goods, just as gold is the most valuable and precious metal.
LW 49:358-359
Thus, Luther’s seal reminds us of three things: (1) It reminds us of the framework we utilise to read the Scriptures—that, as Paul put it, “For I decided to know nothing among you except Jesus Christ and Him crucified” (1 Corinthians 2:2), and that this homiletic of Christ’s work on the cross is what changes human hearts. (2) It reminds us of our confession and identity—that we only preach Christ, not Christ + something else, but solus Christus (Christ alone), and that we are His possession (1 Peter 2:9). And (3) it reminds us to always remain focused on Christ—to always look toward the cross whereupon we receive salvation and eternal life rather than looking inward to ourselves.
The Lutheran Column 