"Having a fresh mental and spiritual attitude]."
We can learn a lot about the importance of a good attitude by looking at the children of Israel.
It's estimated that about 1.5 million Israelites came out of Egypt. God delivered them from slavery and led them to the Promised Land. The trip should have taken about 11 days, but instead it took 40 years. Why? Because they were constantly complaining about everything! They complained about the food God sent from heaven each day. And any time something difficult crossed their path they were ready to give up and go back to Egypt - back to slavery. What's astounding is that out of the 1.5 million people who left Egypt, only two from the original group made it into the Promised Land.
And today there are many Christians who have also escaped from "Egypt" (their former life of slavery to sin), believers who are always looking forward to the Promised Land, yet they end up wandering in the wilderness their entire lives, dealing with the same old problems and issues. Are you one of them? Do you feel like you've been circling the same mountain for too long?
If so, here's your answer: "Strip yourselves of your former nature [put off and discard your old un-renewed self] which characterized your previous manner of life and becomes corrupt through lusts and desires that spring from delusion; And be constantly renewed in the spirit of your mind [having a fresh mental and spiritual attitude], And put on the new nature (the regenerate self) created in God's image, [Godlike] in true righteousness and holiness."
In other words - change your attitude!