Psalms 105:1-3 (NIV):

¹ Give praise to the Lord, proclaim his name;
    make known among the nations what he has done.
² Sing to him, sing praise to him;
    tell of all his wonderful acts.
³ Glory in his holy name;
    let the hearts of those who seek the Lord rejoice.

We sing praises to honor God like the angels in Heaven.  We sing praises no matter the reason or season we are in.  We praise God during good times and bad times.  We sing praises to give God the glory.

In John chapter four, Jesus spoke with the Samaritan woman about living water.  During this conversation, she said that her people worshiped on the mountain where the well was.  It was where their ancestors worshiped.  In verses twenty-one through twenty-four, Jesus explained that the Samaritans worship what they don’t know and salvation comes from the Jews.  In verses twenty-three and twenty-four: ²³ Yet a time is coming and has now come when the true worshipers will worship the Father in the Spirit and in truth, for they are the kind of worshipers the Father seeks. ²⁴ God is spirit, and his worshipers must worship in the Spirit and in truth.

David wrote the word praise several times throughout the book of Psalms.  He either encouraged the Israelites to praise God or praised God himself for all He has done for him,

Paul wrote in First Thessalonians chapter five verses sixteen through eighteen:  ¹⁶ Rejoice always, ¹⁷ pray continually, ¹⁸ give thanks in all circumstances; for this is God’s will for you in Christ Jesus.

We praise to lift God up in song.  We praise to lift our spirits to remind ourselves who God is.  We praise Him to remind us who we are in Jesus Christ.

Paul wrote in Second Corinthians chapter one verses three through five: ³ Praise be to the God and Father of our Lord Jesus Christ, the Father of compassion and the God of all comfort, ⁴ who comforts us in all our troubles, so that we can comfort those in any trouble with the comfort we ourselves receive from God. ⁵ For just as we share abundantly in the sufferings of Christ, so also our comfort abounds through Christ.We also praise God for our blessings. Paul explains this in Ephesians chapter one verses three through ten: ³ Praise be to the God and Father of our Lord Jesus Christ, who has blessed us in the heavenly realms with every spiritual blessing in Christ. ⁴ For he chose us in him before the creation of the world to be holy and blameless in his sight. In love ⁵ he predestined us for adoption to sonship through Jesus Christ, in accordance with his pleasure and will— ⁶ to the praise of his glorious grace, which he has freely given us in the One he loves. ⁷ In him we have redemption through his blood, the forgiveness of sins, in accordance with the riches of God’s grace ⁸ that he lavished on us. With all wisdom and understanding, ⁹ he made known to us the mystery of his will according to his good pleasure, which he purposed in Christ, ¹⁰ to be put into effect when the times reach their fulfillment—to bring unity to all things in heaven and on earth under Christ.

When we worship with our mouths, it is a form of spiritual warfare.  Praising God fights the devil and his attacks against us.