John Calvin Commentary Psalms 119:11

"Thy word have I laid up in my heart, That I might not sin against thee." — Psalms 119:11 (ASV)

I have hid thy word in my heart. Since this psalm was not composed only for the personal and unique use of the author, we can therefore understand that whenever David presents his own example to us, through this model he shows us the path we should follow.

Here we are taught that we are well fortified against Satan's stratagems when God’s law is deeply seated in our hearts. For unless it has a strong and firm hold there, we will readily fall into sin. Among scholars, those whose knowledge is limited to books quickly reveal their ignorance if they do not always have the book before them. In the same way, if we do not truly absorb God's doctrine and become thoroughly familiar with it, Satan will easily surprise and entangle us in his snares.

Our true safeguard, then, lies not in a superficial knowledge of his law, or in a careless reading of it, but in hiding it deeply in our hearts. Here we are reminded that however much people may be convinced of their own wisdom, they still lack all right judgment, unless they have God as their teacher.