The will of God is a descriptive phrase referring to God's plan for their lives. Part of God's will for a Christian is sanctification or being set apart to or dedicated to God. Your defines this sanctifying process as God's will for the readers personally. The application of God's will concerning their sanctification finds expression in three demands. The present tense denotes that Christians are to constantly keep away from fornication.
Fornication translates a comprehensive term denoting every kind of unlawful sexual activity.
To know means to understand how one must act in this matter. Vessel most likely refers to one's own body here. In sanctification and honor means to control one's body in order to bring glory to God. Not in the lust of concupiscence describes a living according to the desires of the flesh. Christians must not allow their desires to dominate them and make them slaves of passion.