To Promoting Truth

May I swear an oath in God's name if I do it reverently?

Yes, 

• when the government demands it,
• or when necessity requires it,
• in order to maintain and promote truth and trustworthiness
• for God's glory and my neighbor's good.
• Such oaths are grounded in God's Word 
• and were rightly used by the people of God 
• in the Old and New Testaments.

May I also swear by saints or other creatures?

No.

• A legitimate oath means calling upon God 
• as the only one who knows my heart to witness
• to my truthfulness
• and to punish me if I swear falsely.
• No creature is worthy of such honor.

For the Bible Tells Me So...

Deuteronomy 6:13 You shall fear the LORD your God and serve Him, and shall take oaths in His name.

Romans 1:9 For God is my witness, whom I serve with my spirit in the gospel of His Son, that without ceasing I make mention of you always in my prayers, 

2 Corinthians 1:23 Moreover I call God as witness against my soul, that to spare you I came no more to Corinth.

Romans 9:1 I tell the truth in Christ, I am not lying, my conscience also bearing me witness in the Holy Spirit,

Matthew 5:34-37 But I say to you, do not swear at all: neither by heaven, for it is God’s throne; 35 nor by the earth, for it is His footstool; nor by Jerusalem, for it is the city of the great King. 36 Nor shall you swear by your head, because you cannot make one hair white or black. 37 But let your “Yes” be “Yes,” and your “No,” “No.” For whatever is more than these is from the evil one.

James 5:12 But above all, my brethren, do not swear, either by heaven or by earth or with any other oath. But let your “Yes,” be “Yes,” and your “No,” “No,” lest you fall into judgment.

The Heidelberg Catechism Lord's Day 37