But they that wait upon the Lord shall renew their strength; they shall mount up with wings as eagles; they shall run, and not be weary; and they shall walk, and not faint. (Isaiah 40:31)
That is, look to the Lord in sincerity and humility for wisdom and strength, and then patiently await His guidance (see on ch. 30:21; cf. 57:15).
Renew their strength.
The Christian life is a constant process of receiving from God and giving to God. Strength is expended in service for the Master (cf. Mark 5:30), but there are always new supplies of grace and vitality available from Him who knows not weariness. He who does not continue to receive strength from God will soon find himself in a position where he is unable to serve God. See DA 827.
As eagles.
One of the most magnificent sights of the wild is an eagle soaring in the sky, higher and higher, with seemingly little effort. Similarly, the child of God who draws his strength from above is enabled to go ever onward and upward, always reaching new heights of achievement (see Ps. 103:5). Day after day it is the privilege of the Christian to go on from grace to grace and from victory to victory (see 1 Cor. 15:57; 2 Cor. 2:14; Ed 18; DA 679). Strength is added to strength, and progress is constant. Higher and still higher goals come into view, and eventually the Christian attains to “the prize of the high calling of God in Christ Jesus” (Phil. 3:14).