Hi, Bill!
…it’s quite similar to every day’s meaning: you state, from your heart, what you know is True.
…the difference is that you are being Christ’s witness; as the “good” thief on the cross acknowledged Christ’s Divinity and confessed his and our unrighteousness. He stood for Christ and denounced himself.
Christ is telling us that we must Stand for Him when our time comes; that we are not to attempt to embellish or prepare speeches for it is the Holy Spirit Who will Speak through us to bring the Word of God even to those who persecute us. Our job/function is to Stand Firm and give reason for our Faith.
DISCLAIMER: Catholic Answers has turned over the archive to Catholic-Questions.org and no longer owns, manages, or moderates the forums. For additional apologetics resources please visit www.catholic.com.