We're told not to 'lift up our soul to what is false' or 'swear deceitfully.' What kind of 'false' things are we tempted by?
The second part of the verse addresses our deepest affections and our words. 'Who has not lifted up his soul to what is false' means not directing your ultimate desire and devotion towards anything other than God. This 'vanity' can refer to idols, worldly possessions, status, or anything that takes the place of God in your heart. It’s about where your true 'want' lies.
'And does not swear deceitfully' speaks to the integrity of our words, especially when we make solemn commitments or take oaths. It means being truthful and not using words to manipulate, cheat, or mislead others. Our speech should reflect the truthfulness of the God we serve.