"Why is giving thanks to God important?

The Bible is filled with commands to give thanks to God (Psalm 106:1;
107:1; 118:1; 1 Chronicles 16:34; 1 Thessalonians 5:18). Most verses
go on to list reasons why we should thank Him, such as "His love
endures forever" (Psalm 136:3), "He is good" (Psalm 118:29), and "His
mercy is everlasting" (Psalm 100:5). Thanksgiving and praise always go
together. We cannot adequately praise and worship God without also
being thankful.

Feeling and expressing appreciation is good for us. Like any wise
father, God wants us to learn to be thankful for all the gifts He has
given us (James 1:17). It is in our best interest to be reminded that
everything we have is a gift from Him. Without gratefulness, we become
arrogant and self-centered. We begin to believe that we have achieved
everything on our own. Thankfulness keeps our hearts in right
relationship to the Giver of all good gifts.

Giving thanks also reminds us of how much we do have. Human beings are
prone to covetousness. We tend to focus on what we don't have. By
giving thanks continually we are reminded of how much we do have. When
we focus on blessings rather than wants, we are happier. When we start
thanking God for the things we usually take for granted, our
perspective changes. We realize that we could not even exist without
the merciful blessings of God.

First Thessalonians 5:18 says, "In everything give thanks; for this is
God's will for you in Christ Jesus." We are to be thankful not only
for the things we like, but for the circumstances we don't like. When
we purpose to thank God for everything that He allows to come into our
lives, we keep bitterness at bay. We cannot be both thankful and
bitter at the same time. We do not thank Him for evil, but that He is
sustaining us through it (James 1:12). We don't thank Him for harm He
did not cause, but we thank Him when He gives us the strength to
endure it (2 Corinthians 12:9). We thank Him for His promise that "all
things will work together for the good, to those who love God and are
called according to His purpose" (Romans 8:28).

We can have thankful hearts toward God even when we do not feel
thankful for the circumstance. We can grieve and still be thankful. We
can hurt and still be thankful. We can be angry at sin and still be
thankful toward God. That is what the Bible calls a "sacrifice of
praise" (Hebrews 13:15). Giving thanks to God keeps our hearts in
right relationship with Him and saves us from a host of harmful
emotions and attitudes that will rob us of the peace God wants us to
experience (Philippians 4:6–7).