Continue in What You Have Learned and Firmly Believed

I will meditate on your precepts

and fix my eyes on your ways.

I will delight in your statutes;

I will not forget your word.  (Psalm 119:15-16)

[W]e should feel sufficiently constrained by the command of God alone, who solemnly commands in Deuteronomy 6:6ff that we should always meditate upon His precepts, sitting, walking, standing, lying down, and rising, and have them before our eyes and in our hands as a constant mark and sign.  Doubtless He did not so solemnly require and enjoin this without a purpose; but because He knows our danger and need, as well as the constant and furious assaults and temptations of devils, He wishes to warn, equip, and preserve us against them, as with a good armor against their fiery darts and with good medicine against their evil infection and suggestion.  Oh, what mad, senseless fools are we that, while we must ever live and dwell among such mighty enemies as the devils are, we nevertheless despise our weapons and defense, and are too lazy to look at or think of them!

Martin Luther, Large Catechism: Introduction 14-15