That is 'I testify or charge thee before God, and by the appearing.' 'By' may be taken as 'according to,' that is, the judgment is according to the power and glory of his appearing and his kingdom. Some authorities read 'at.'
Or 'will be turned aside,' or 'have turned themselves aside.' Compare 1Tim. 1.6; 5.15. Here their being already turned aside leads them to turn away their ear from the truth.
This implies, not watching actively, nor being awake, but that sober clearness of mind resulting from exemption from false influences -- not muddled with the influence of what intoxicates. So we think of one when we say, He has a sober judgment.