But the salvation of the righteous is of the LORD: He is their strength in the time of trouble. -Psalm 37:39

…and as thy days so shall thy strength be. -Deuteronomy 33:25

The strength which is here promised is to abide through days. “As thy days, so shall thy strength be.” Not for today only, but for tomorrow, and for every day as every day shall come. The longest and the shortest day, the brightest and the darkest day, the wedding and the funeral day, shall each have its strength measured out till there shall be no more days. The Lord will portion out to His saints their support even as their days follow each other.

“Days of trial, days of grief,
In succession thou may’st see;
This is still thy sweet relief,
‘As thy day, thy strength shall be.'”

This strength is to be given daily We shall never have two days’ grace at a time.

“Day by day the manna fell:
Oh, to learn this lesson well,
‘Day by day’ the promise reads:
Daily strength for daily needs!”

“As thy days, so shall thy strength be”: this secures you a day’s burden and a day’s help, a day’s sorrow and a day’s comfort. After all, what more do we want?… Let us narrow our vision as to the necessities of daily life, not looking so far ahead as to compress into today more evil than naturally belongs to it; for “Sufficient unto the day is the evil thereof.” Our strength is to be given to us daily. ~ C.H. Spurgeon

https://www.blueletterbible.org/Comm/spurgeon_charles/sermons/2062.cfm