Psalm 37:24 Though he fall, he shall not be utterly cast down: for the Lord upholdeth him with his hand.
David admits that a righteous man may fall on the path of life, or even stray from it, but the promise is that he will not be utterly cast down. Because we are corrupted sinners falls, stumbles, and failures will occur while walking the path through this life to heaven. But the Holy Spirit who lives within the faithful believer will be there to pick him up, hold him up, and keep him going.
The bad news is: we fall. The Good News: the Lord holds us up. That does not give us license to go ahead and sin for we will be forgiven anyway; instead the gospel message renews life and hope and gives us the desire and motivation not to fall again. Because we are fully saint, the Holy Spirit within forgives the cause of the fall and picks us up again, and again.