The Hebrew verb yashar means to be or make straight, level, or right. It describes the quality of moral uprightness, directness, and integrity. Its adjectival form yashar and noun yosher are used extensively in wisdom literature and the Psalms to characterize the person whose ways are aligned with God's will.
Yashar is one of the key Hebrew terms for moral character. 'What is right in the eyes of the LORD' (ha-yashar be-einei YHWH) is a recurring covenantal standard in Deuteronomy and the historical books. The book of Proverbs describes wisdom as making paths straight (3:6), and Isaiah's preparation passage ('make straight in the desert a highway for our God,' Isaiah 40:3) uses the same concept to announce the Messiah's coming. John the Baptist applied this prophecy directly to his ministry. The New Testament fulfillment shows that true moral straightness — righteousness — comes through Christ who is 'the way' (John 14:6).