The everlasting God Neither faints nor is weary.

Isaiah 40:28
The everlasting God, the Lord, The Creator of the ends of the earth, Neither faints nor is weary.

The context of this quote is in the chapter of Isaiah which is delivered to comfort the children Israel and God's people throughout the generations. Have we ever thought that God did not hear us when are petitions and prayers are not answered? This may lead to the reasoning that God is too busy with too many other people (wrongly thinking God is limited) or that our matters are not important enough (wrongly putting down our own worth with respect to God).

The Scripture assures us God does not get tired. He has the infinite power to sustain us, gives strength and power to the weak. Our part is that we must wait on God and believing on God's promises is faith, rather than just believing on His existence like heathens do. To those who believe and wait, He promises:
"They shall mount up with wings like eagles,
They shall run and not be weary,
They shall walk and not faint."

For You have been a Shelter for Me

David describes God as his strong tower and shelter. He commits himself to live under God's tabernacle and under the shelter of His wings. He has the assurance that God will sustain him and many generations after him.

Psalm 61
To the Chief Musician. On a stringed instrument.[a]A Psalm of David.

 1 Hear my cry, O God;
         Attend to my prayer.
 2 From the end of the earth I will cry to You,
         When my heart is overwhelmed;
         Lead me to the rock that is higher than I.
        
 3 For You have been a shelter for me,
         A strong tower from the enemy.
 4 I will abide in Your tabernacle forever;
         I will trust in the shelter of Your wings.  Selah 
        
 5 For You, O God, have heard my vows;
         You have given me the heritage of those who fear Your name.
 6 You will prolong the king’s life,
         His years as many generations.
 7 He shall abide before God forever.
         Oh, prepare mercy and truth, which may preserve him!
        
 8 So I will sing praise to Your name forever,
         That I may daily perform my vows.