The psalmist is diligent. Notice his words — a kind of two-step direction in his diligence:
147 I rise before dawn and cry for help;
I put my hope in your words.
148 My eyes are awake before each watch of the night,
that I may meditate on your promise.
Morning and at intervals during the night the psalmist first:
Cries for help (once again, like vv. 145-146) and second:
Meditates on God’s promise (uttered promises).
He cries and he meditates. He does it all night long and early in the morning. What does he do it for?
It appears to me that v. 147 shows what his diligence was directed at: “hope in your words.” The meditation then of v. 148 is probably not simply Torah-study but meditation on God’s words in order to find comfort during his oppression.
The psalmist’s hope of deliverance is so he can continue his life of obedience to the Lord.