How does the Psalm contrast the fleeting nature of human life and gods eternal existence in Psalm 102?

In Psalm 102, the psalmist contrasts the transient nature of human life with God's eternal existence by highlighting human suffering and mortality. The psalmist laments that human days are like grass, which withers and fades away, emphasizing the brevity of life. In stark contrast, God is depicted as eternal, unchanging, and sovereign, whose years will never end. This juxtaposition serves to remind the faithful of their reliance on God's everlasting nature amidst their own temporal struggles.