In Matthew 5:34, Jesus explicitly forbids swearing by heaven because it is God's throne — the same reasoning behind the condemnation here.

Isaiah 66:1 states heaven is God's throne, directly underlying Jesus' point that swearing by heaven invokes God Himself.

Acts 7:49 quotes Isaiah 66:1 ('Heaven is my throne'), reinforcing the same truth that heaven belongs to God — confirming the seriousness of swearing by it.

Psalm 11:4 declares that the LORD's throne is in heaven, providing the OT foundation for calling heaven God's throne in this oath context.

Revelation 4:2 shows John seeing a throne in heaven with God seated on it — the very reality Jesus says is invoked when swearing by heaven.