And the angel of the LORD said unto him, Why askest thou thus after my name, seeing it is secret?

Wesley's Notes

13:18 Secret - Hidden from mortal men: or, wonderful, such as thou canst not comprehend: my nature and essence, (which is often signified by name in scripture) is incomprehensible. This shews, that this was the angel of the covenant, the Son of God.

King James Translators' Notes

secret: or, wonderful

Matthew Henry's Concise Commentary

13:15-23 What Manoah asked for instruction in his duty, he was readily told; but what he asked to gratify his curiosity, was denied. God has in his word given full directions concerning our duty, but never designed to answer other questionings. There are secret things which belong not to us, of which we must be quite contented to be ignorant, while in this world. The name of our Lord is wonderful and secret; but by his wonderful works he makes himself known as far as is needful for us. Prayer is the ascent of the soul to God. But without Christ in the heart by faith, our services are offensive smoke; in him, acceptable flame. We may apply this to Christ's sacrifice of himself for us; he ascended in the flame of his own offering, for by his own blood he entered in once into the holy place, Heb 9:12. In Manoah's reflections there is great fear; We shall surely die. In his wife's reflection there is great faith. As a help meet for him, she encouraged him. Let believers who have had communion with God in the word and prayer, to whom he has graciously manifested himself, and who have had reason to think God has accepted their works, take encouragement from thence in a cloudy and dark day. God would not have done what he has done for my soul, if he had designed to forsake me, and leave me to perish at last; for his work is perfect. Learn to reason as Manoah's wife; If God designed me to perish under his wrath, he would not give me tokens of his favour.