The Chief Priests of Jerusalem would certainly have been aware what it meant to be ‘in spirit’ and believed THEY knew The Father…
But Jesus told them: had they known the Father, they would know Him also; and that ‘they know not what they do’ when He asked forgiveness for them of His Father; of God Himself.
It is easy for us to fool ourselves we are being ‘righteous’ and ‘in spirit’ when we are actually moving slowly, day-by-day, away from Him, from His Spirit.
WE need to be ever watchful of where our spirit (and our Heart) is leading us. If it is leading us away from the Truth in His Word then we need to re-adjust ourselves and not continue in our self (flesh) assured foolishness. If we are not doing as He commands (loving HIM with all we are, loving all others equally, forgiving, doing unto all others as we would have done unto us, etc) then we know we need to adjust. To correct our course and our spiritual ‘compass’…. back to that of the True ‘North’ (not moving instead towards the ‘East’, or the ‘West’) But ‘straight Up’.