Every good thing given and every perfect gift is from above, coming down from the Father of lights, with whom there is no variation or shifting shadow.

God is steadfast and so, too, we should be... in Him:

Therefore, my beloved brethren, be steadfast, immovable, always abounding in the work of the Lord, knowing that your toil is not in vain in the Lord. - 1 Cor 15:58

In the Al Hatzadikim portion of the Shemonei Esrei prayers we declare "Blessed are You, HaShem, Mainstay and Assurance of the righteous."

He is our Mainstay and our Assurance... because He is steadfast and unchanging.