"Giving thanks always for all things unto God and the Father in the name of our Lord Jesus Christ." (Ephesians 5:20)
Being thankful for everything that happens in his or her life to a Christian believer is listed in this section of Paul's letter to the Ephesians as one of the evidences that a Christian is indeed "filled with the Spirit" (Ephesians 5:18).
That is not all. Not only for everything, but in everything, we should give thanks to God. "In every thing give thanks: for this is the will of God in Christ Jesus concerning you" (1 Thessalonians 5:18).
These two commands are easy to obey when the living is easy, as the song says, though we might easily forget to do so. But when the Lord is allowing us to hurt for a while, thanksgiving becomes hard. It is hard while we are experiencing the difficulty and just as hard when it has passed with no relief in sight. The two small prepositions "in" and "for" are different in New Testament Greek as well as in modern English, and God really wants us to learn how to thank Him both during and after the hard experience.
Because He has allowed it for a good purpose! The apostle James urges us to "count it all joy when ye fall into divers temptations" (that is, "various testings"); "Knowing this, that the trying of your faith worketh patience. But let patience have her perfect work, that ye may be perfect and entire, wanting nothing" (James 1:3-4). Paul says that we can even "glory in tribulations also: knowing that tribulation worketh patience; And patience, experience; and experience, hope: And hope maketh not ashamed; because the love of God is shed abroad in our hearts by the Holy Ghost which is given unto us" (Romans 5:3-5). Patience and real love will come to characterize an habitually thankful Christian. HMM