So I always take pains to have a clear conscience toward both God and man.
I have always been struck by the power of this statement of Paul's. For a while in my teen and college years I considered this my "life verse", when having a "life verse" was a required part of the Christian calling card. Paul says this to the Roman governor Felix as he defends his very life before the Jewish authorities who have conspired to see him dead. It is a powerful belief by which to live, but today as I look at it, it strikes me that it is the beliefs behind this motto that are what give it such strength.
Paul sets forth his faith behind this motivation to have a clean conscience toward God and man with the following five belief statements that proceed verse sixteen:
1) I am a Christian, a follower of the Way (14).
2) I worship the God Who is the same God of the Jews (14).
3) I believe the Jewish scriptures in their entirety (14).
4) I place my hope in God (15).
5) I believe in the resurrection of all people. just and unjust (15).
These beliefs informed Paul's desire to have a clear conscience. They were what he was defending and in a wise move on his part, these were also statements (except for #1) that the Jewish Pharisees would affirm. What Paul is thus saying is that their dispute with him is over one issue: Jesus, Someone about Whom Luke tells us in the context that Felix has accurate knowledge (Acts 24:20). Felix knows the Jesus story and the resultant birth of the church accurately. Paul has put the gospel at the forefront in this hearing. He cannot help but preach Christ!
It seems then that Paul's meaning of having a clear conscience before God and man indicates that his conscience will be clear with God first. By making the gospel the issue at his trial, Paul does that brilliantly. I see then, that if ever this hopeful motto could mark my life, I too must let the gospel, let my Savior, lead first in my thoughts, attitudes, statements, language, and actions.