Contradiction with 1 Samuel 16:7
This verse emphasizes that the Lord looks at the heart, not outward appearances or public ordination, which contrasts with the act of publicly designating a leader as done in Numbers 27:19.
1 Samuel 16:7: But the LORD said unto Samuel, Look not on his countenance, or on the height of his stature; because I have refused him: for [the LORD seeth] not as man seeth; for man looketh on the outward appearance, but the LORD looketh on the heart. [outward...: Heb. eyes]
Contradiction with Jeremiah 17:5
This verse warns against putting trust in man, whereas Numbers 27:19 involves trusting in Joshua through a formal laying of hands.
Jeremiah 17:5: Thus saith the LORD; Cursed [be] the man that trusteth in man, and maketh flesh his arm, and whose heart departeth from the LORD.