In the beginning you laid the foundations of the earth and the heavens are the work of your hands (Psalm 102:25).
The great truth that we are taught here is that God is unchangeable.
This means that He is ever reliable. He is the Rock, the One on whom we can always depend.
One of the problems with human beings is that sometimes we can change for the worse. Sometimes even the most reliable people can let you down—they can fail to fulfill what they've promised. There can be many reasons for this, but basically it's because they've changed. As we get older our memories begin to fail and sometimes people forget about their promises. Sometimes we get sick and are unable to fulfill our word. Sometimes they die and thus they're totally unable to fulfill what they promised. Sometimes a person's attitude toward you will change and they fail to carry out their word. Change affects every one of us.
But we should understand that our God is not like that. He is unchangeable. It is very important that we properly understand this attribute of God because this knowledge can be a great source of strength to us in times of trouble.