What does it mean for the idols to speak vanity?

In Zechariah 10:2, the phrase 'idols have spoken vanity' reveals that anything which distracts from the true worship of God is ultimately without substance or value. This includes both physical idols and intangible idols like self-perceived righteousness. Such idols provide false comfort and lead individuals away from recognition of their need for God's grace. The futility of these idols is evident in that they cannot fulfill the promises they represent, rendering them devoid of truth. The passage urges believers to seek God, who alone provides real blessings and comfort through Christ.