Nay, but you shall serve Allah alone and be among those who show gratitude for His Guidance and Bounties by sharing them with others. ('Shukr' = Gratitude = Keeping Allah's bounties open for the benefit of others thus obtaining best possible and collective results. It does not end with just verbal 'Thank God!'
No, serve only Allah and be of those who are thankful (evaluate the blessing of what it means to be a servant)!
Al-muntakhab fi tafsir al-Qur'an al-Karim
Do not pay attention to the infidels' irreverent exhortation. It is only Allah Whom you are enjoined to worship and be among those who impel themselves to the feeling of gratitude and gratefulness