I will praise the name of God with a song; I will magnify him with thanksgiving. (Psalm 69:30)
There are two kinds of magnifying: microscope magnifying and telescope magnifying. The one makes a small thing look bigger than it is. The other makes a big thing begin to look as big as it really is.
When David says, “I will magnify God with thanksgiving,” he does not mean: “I will make a small God look bigger than he is.” He means: “I will make a big God begin to look as big as he really is.”
We are not called to be microscopes, but telescopes. Christians are not called to be con-men who magnify their product out of all proportion to reality, when they know the competitor's product is far superior. There is nothing and nobody superior to God. And so the calling of those who love God is to make his greatness begin to look as great as it really is.
The whole duty of the Christian can be summed up in this: feel, think, and act in a way that will make God look as great as he really is. Be a telescope for the world of the infinite starry wealth of the glory of God.
This is what it means for a Christian to magnify God. But you can't magnify what you haven’t seen or what you quickly forget.
Therefore, our first task is to see and to remember the greatness and goodness of God. So we pray to God, “Open the eyes of my heart,” and we preach to our souls, “Soul, forget not all his benefits!”