8 Therefore, anyone who rejects this instruction does not reject a human being but God, the very God who gives you his Holy Spirit.

Read 1 Thessalonians 4:8 Using Other Translations

He therefore that despiseth, despiseth not man, but God, who hath also given unto us his holy Spirit.
Therefore whoever disregards this, disregards not man but God, who gives his Holy Spirit to you.
Therefore, anyone who refuses to live by these rules is not disobeying human teaching but is rejecting God, who gives his Holy Spirit to you.