May we then swear religiously by the name of God?

Heidelberg Catechism (extended)

The Catechism
Method of Instruction in the Christian Religion
As the Same is Taught in the Reformed Churches and Schools

(with the Scripture references written out)

Note. This Catechism is fully based on the Scriptures. The references to Scripture are indicated in parentheses with a letter. For example, the letter (a) points to the texts (a) placed after the answer.

37. Lord's Day 

Q. 101. May we then swear religiously by the name of God? 

A. Yes: either when the magistrates demand it of the subjects; or when necessity requires us thereby to confirm a fidelity and truth to the glory of God, and the safety of our neighbour: for such an oath is founded on God's word, (a) and therefore was justly used by the saints, both in the Old and New Testament. (b) 

(a) Deut.6:13 Thou shalt fear the LORD thy God, and serve him, and shalt swear by his name. Deut.10:20 Thou shalt fear the LORD thy God; him shalt thou serve, and to him shalt thou cleave, and swear by his name. Isa.48:1 Hear ye this, O house of Jacob, which are called by the name of Israel, and are come forth out of the waters of Judah, which swear by the name of the LORD, and make mention of the God of Israel, but not in truth, nor in righteousness. Heb.6:16 For men verily swear by the greater: and an oath for confirmation is to them an end of all strife. 

(b) Gen.21:24 And Abraham said, I will swear. Gen.31:53 The God of Abraham, and the God of Nahor, the God of their father, judge betwixt us. And Jacob sware by the fear of his father Isaac. Gen.31:54 Then Jacob offered sacrifice upon the mount, and called his brethren to eat bread: and they did eat bread, and tarried all night in the mount. Jos.9:15 And Joshua made peace with them, and made a league with them, to let them live: and the princes of the congregation sware unto them. Jos.9:19 But all the princes said unto all the congregation, We have sworn unto them by the LORD God of Israel: now therefore we may not touch them. 1 Sam.24:22 And David sware unto Saul. And Saul went home; but David and his men gat them up unto the hold. 2 Sam.3:35 And when all the people came to cause David to eat meat while it was yet day, David sware, saying, So do God to me, and more also, if I taste bread, or ought else, till the sun be down. 1 Kin.1:28 Then king David answered and said, Call me Bathsheba. And she came into the king's presence, and stood before the king. 1 Kin.1:29 And the king sware, and said, As the LORD liveth, that hath redeemed my soul out of all distress, 1 Kin.1:30 Even as I sware unto thee by the LORD God of Israel, saying, Assuredly Solomon thy son shall reign after me, and he shall sit upon my throne in my stead; even so will I certainly do this day. Rom.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 Cor.1:23 Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth. 

Q. 102. May we also swear by saints or any other creatures? 

A. No; for a lawful oath is calling upon God, as the only one who knows the heart, that he will bear witness to the truth, and punish me if I swear falsely; (a) which honour is due to no creature. (b) 

(a) 2 Cor.1:23 Moreover I call God for a record upon my soul, that to spare you I came not as yet unto Corinth. Rom.9:1 I say the truth in Christ, I lie not, my conscience also bearing me witness in the Holy Ghost, 

(b) Matt.5:34 But I say unto you, Swear not at all; neither by heaven; for it is God's throne: Matt.5:35 Nor by the earth; for it is his footstool: neither by Jerusalem; for it is the city of the great King. Matt.5:36 Neither shalt thou swear by thy head, because thou canst not make one hair white or black. James 5:12 But above all things, my brethren, swear not, neither by heaven, neither by the earth, neither by any other oath: but let your yea be yea; and your nay, nay; lest ye fall into condemnation.

Source: http://www.ccel.org/creeds/heidelberg-cat-ext.txt