As Christians, we are commanded to utilize the Psalms:

Speaking to one another in psalms and hymns and spiritual songs,
singing and making melody in your heart to the Lord,  (Ep 5:19)

Let the word of Christ dwell in you richly in all wisdom,
teaching and admonishing one another in psalms and hymns and
spiritual songs, singing with grace in your hearts to the Lord.
(Col 3:16)

Is anyone among you suffering? Let him pray. Is anyone cheerful?
Let him sing psalms.  (Jm 5:13)

Thus the Psalms are useful for singing praises to God.  They are also
useful for teaching and confirming that Jesus is the Christ or Messiah.
Note the use Jesus made of them (Lk 24:44-47), and also Peter’s use of
them in his first gospel sermon (Ac 2:25-28,34-35).

It has been said that in the Psalms one finds “expressed the eager
yearning and longing for God’s presence”.  It certainly contains
“prayers and songs of joyous trust and praise.”  Indeed, every emotion
known to man is expressed in beautiful and inspired terms (e.g., joy,
anger, praise, repentance, trust, even doubt).  Filled with some
emotion for which you cannot find the words to express it?  It is
likely you will find it expressed in the book of Psalms!

I would therefore suggest that the Psalms are capable of serving as:

* The Christian’s “hymnal” to assist us in our praise to God

* The Christian’s “prayer book” in which we learn how to approach
God in prayer

* The Christian’s “book of evidences” to strengthen our faith in
Jesus Christ

* The Christian’s “training guide” for living holy and righteous
lives before God