This is still about the genuineness of our approach to God and avoiding making insincere commitments to God. Don’t commit yourself to something you don’t know how to do.
Knowing how unstable human nature is and yet how blind man is to his weakness, Solomon fears that we will underestimate our own tendency to utter vain words before God. He urges us to examine ourselves and realise what is at stake. We must banish that overconfidence that is part of our fallen nature and understand that it is not within our capacity to come to God correctly. We must cry out to God for help, because there is danger ahead if we proceed in a flippant manner. There are consequences to making half-hearted vows to God.