I Corinthians 1:6

Even as the testimony of Christ was confirmed in you (KJV)

Then: Nothing can be more comforting than to have someone else see Christ in you. It removes self-doubt. It removes concern that maybe something is the matter with your rock solid belief that Jesus is the Christ, risen from the dead, the Son of God. And to have Paul, an apostle, thanking God for your belief has to be a major epitome of God's grace to you. The verse is also another statement of the past event which N. T. Wright (p.4) calls a "messianic message." Christ is evident in the Corinthians because his name is readily spoken in love for him, in prayer through him, and friendship with him. Matthew Henry infers that "testimony" means the presence of signs of wonders which verify the doctrine of Christ. In such instances believers maintained deep fellowship with Christ and with each other.

Now: In times when the bond with Christ is solid, prayers answered, peace and grace abide, a believer doesn't need outside confirmation of his/her Christ-like image. But on days when faith wobbles and doubt intervenes, a friendly statement about obvious choices to serve the Lord by upholding his standards go a long way to removing self-doubt. A continuous, thankful review of all God's past work in our lives, lives of friends, and life of our church can return faith to its solid state. It orders our memories and our priorities. It becomes a major part of fellowship with Christ and other believers.

Extra Source: Commentary on the Whole Bible (Acts to Revelation) by Matthew Henry, see: http://www.ccel.org/ccel/henry/mhc6.iCor.ii.html

1 Corinthians 1:5

That in every thing ye are enriched by him, in all utterance, and in all knowledge (KJV)

Then: Called in the past, the Corinthians are so enriched in the present they are both knowledgeable and able to tell others about Christ. This is a gift based on grace for which one can be truly thankful. N. T. Wright (p.4) believes the verse indicates great ability for these believers to teach one another and in doing so, strengthen and confirm each others faith. Dr. Magness considers the enrichment, calling, and Christ's confirmation to be a "past" event in the believer's life, even though it allows for a present action. Wesley notes a hidden meaning mixed in with Paul's thankfulness. In referring to "knowlege" and "utterance," Paul picks out two attributes and skills greatly admired in and by the liberal Corinthians. Honored by Paul's indirect praise, they are later more willing to understand why these gifts must be both channeled and utilized in glorifying God, not themselves. Serving the Lord well is their unending goal.

Now: Serving the Lord well is our unending goal. By elevating thankfulness to a top priority, today's believers learn much. Being thankful for the knowledge and ability to tell others about our experiences puts a right priority on the values of teaching one another, strengthening one another and confirming one another. Unfortunately, being Corinthian comes just as naturally as in New Testament times. Proud of church heritage, proud of knowledge, proud of skills, there we stand oblivious to the blight and disease of pride growing on what were meant to be wonderful gifts. Thanksgiving can strip away the fungus, cut out the spots, and let God's grace shine through again.
Added source: Wesley's Notes on the Bible http://www.ccel.org/ccel/wesley/notes.i.viii.ii.html

I Corinthians 1:4

I thank my God always on your behalf, for the grace of God which is given you by Jesus Christ (KJV)

Then: Letter element #4 coming through in five verses -- thanksgiving. Verse 4 concentrates on God's faithfulness in the past. Dr. Magness suggests readers note the "who, when, what and why" answers. Who? Paul thanks God. (He decides to include thanks to God from the Corinthians.) When? Always? What? God's grace sent to the Corinthians by Christ. N. T. Wright advises readers that Paul is sneaking in thoughts of the letter's coming topics. Grace is important and just can't be taken for granted. Thanking God for it helps recipients develop an accurate Christian world view. A basic understanding of grace underlies an attitude of being open to God's teachings.

Now: It is easy for 21st materialistic-centered Christians to take God's gifts for granted. Those without the sharp perception that grace comes from the Lord may become proud. That attitude produces churches which wither and die. The ones who recognize the source and substance of the gift can and do minister successfully. Taking time to give thanks gives glory to God at the same time that it structures great attitudes about work in the church. Conclusion: Take time to thank God.