Being in this world but not of this world. Say no to ungodliness and yes to all that delights the Lord. All this makes part of sanctification, which is described in this Psalm as a tree which is deeply rooted beside streams of water. Implying that a life seeking holiness, will be secure, strong (unshakable) and most of all able to bear good fruit. The fruit of the spirit.
On the other hand there are those who choose to ignore the Word of God or who are unwilling to let go of the pleasures of this world. If they persist in this life, judgement is assured over them, described in this psalm as chaff in the wind, implying powerless will, unprotected, vulnerable, no sense of purpose and direction.
The psalm ends with a promise. The paths of those who pursue holiness and rightousness will be secured in the Lord’s protection, while those who choose to remain unrepented will be heading to ruins. A life leading to a dead end and eternal damnation.