Albert Barnes Commentary Matthew 23:22

"And he that sweareth by the heaven, sweareth by the throne of God, and by him that sitteth thereon." — Matthew 23:22 (ASV)

The throne of God. Heaven is his throne (Matthew 5:34). It is so called because it is the place where he sits in glory. Jesus says, here, that all who swear at all, do in fact swear by God, or the oath is good for nothing. To swear by an altar, a gift, or a temple has no force, unless it is meant to appeal to God himself. The essential thing in an oath is calling God to witness our sincerity. If a real oath is taken, therefore, God is appealed to. If not, it is foolish and wicked to swear by anything else.