I’ve written on Matthew 10:16 before, but with regard to broader misunderstandings about Christianity. This time thought I’d bring up another misunderstanding in the Christian life that is related directly to interpretation of this passage. I’ve heard Matthew 10:19-20 used to say that preparing for evangelism or studying the Bible academically is bad. This misconception can be resolved by paying careful attention to Matthew 10:16, but a resolution of the difficulty can be made by looking carefully at verses 19 and 20 as well:
16 Behold, I am sending you as sheep in the midst of wolves. Therefore, be as wise as serpents and as innocent as doves. 17 Now, beware of people. For they will hand you over to the Sanhedrin, and in their synagogues they will flog you; 18 then they will bring you before rulers and kings because of me in order to be a testimony to them and the nations. 19 Now, when they hand you over, do not be anxious over how you will speak or what you will say; for what you will say in that hour will be given to you. 20 For you are not the ones speaking, but the Spirit of your Father speaks by you. (Matthew 10:16-20) 
If the claim being made is “In Matthew 10:19-20 Jesus says that the Holy Spirit will give you what to say and not to think about what to say when you share the gospel.” Then these observations in the text itself provide counter evidence to that claim:
- In 10:18, the disciples will be a testimony. In the New Testament, that word group is typically used to mean testimony to the facts of the case regarding Jesus. In other words, Jesus expects his disciples to communicate the material in the Sermon on the Mount and Jesus’ announcement of God’s kingdom in his ministry as well
- Jesus says, “do not be anxious over how you will speak or what you will say.” This is not the same thing as saying, “do not think.” Do not be anxious means, do not obsess over it to the point of not making any decision to speak (see how Matthew 6 shows that Jesus’ teaching on anxiety about tomorrow assumes that his disciples will be working and planning for tomorrow).
- Finally, in John’s gospel, Jesus says that the Holy Spirit will “remind you of everything which I said to you. (John 14:26)”
Any interpretation of Scripture that implies that reflection on your life or on the gospel is a negative thing should probably be viewed with skepticism.
 Kurt Aland et al., Novum Testamentum Graece, 28th Edition. (Stuttgart: Deutsche Bibelgesellschaft, 2012), Mt 10:16–20. “16 Ἰδοὺ ἐγὼ ἀποστέλλω ὑμᾶς ὡς πρόβατα ἐν μέσῳ λύκων· γίνεσθε οὖν φρόνιμοι ὡς οἱ ὄφεις καὶ ἀκέραιοι ὡς αἱ περιστεραί.
17 Προσέχετε δὲ ἀπὸ τῶν ἀνθρώπων· παραδώσουσιν γὰρ ὑμᾶς εἰς συνέδρια καὶ ἐν ταῖς συναγωγαῖς αὐτῶν μαστιγώσουσιν ὑμᾶς· 18 καὶ ἐπὶ ἡγεμόνας δὲ καὶ βασιλεῖς ἀχθήσεσθε ἕνεκεν ἐμοῦ εἰς μαρτύριον αὐτοῖς καὶ τοῖς ἔθνεσιν. 19 ὅταν δὲ παραδῶσιν ὑμᾶς, μὴ μεριμνήσητε πῶς ἢ τί λαλήσητε· δοθήσεται γὰρ ὑμῖν ἐν ἐκείνῃ τῇ ὥρᾳ τί λαλήσητε· 20 οὐ γὰρ ὑμεῖς ἐστε οἱ λαλοῦντες ἀλλὰ τὸ πνεῦμα τοῦ πατρὸς ὑμῶν τὸ λαλοῦν ἐν ὑμῖν.”