John MacArthur comments that “swearing by those things [temple, altar, and so on] is tantamount to swearing by God Himself” (The MacArthur Bible Commentary, p. 1,169). Any godly commitment we make must be honored, for the Lord prizes truth and fidelity. If you tend not to follow through on your promises, consider whether you are making more of them than you can keep. Pledge to do only those things you know you have time to fulfill.
For further study:
The Bible in a year: