From an evangelical Christian perspective, the most likely author of Psalm 139:13-14 is King David. David is traditionally attributed as the author of many of the Psalms, including Psalm 139, based on both internal evidence within the text and external historical sources.

Psalm 139 is a deeply personal and introspective meditation on God’s intimate knowledge and care for each individual. The language used in the Psalm reflects David’s own experiences and struggles, such as his time as a shepherd and his reign as king. Additionally, the themes of praise, trust, and reliance on God are consistent with David’s character as depicted in the Bible.

Furthermore, the New Testament also attributes the authorship of Psalm 139 to David. For example, in Acts 4:25-26, the early Christians quote Psalm 2, attributing it to David, which suggests a tradition of Davidic authorship for the Psalms.

Overall, while the authorship of the Psalms is not definitively proven, most evangelical Christians believe that King David was the likely author of Psalm 139:13-14 based on both the internal evidence within the text and external historical sources.