Then shall thou walk in thy way safely. The first of the promises of protection, which follow from Proverbs 3:23-26. He who keeps "sound wisdom and discretion" shall enjoy the greatest sense of security in all situations of life.
Safely (lavetakh); either in confidence, as Vulgate fiducialiter, i.e. confidently, because of the sense of security (cf. LXX; πεποιθὼς ἐν εἰρήνῃ, and Proverbs 3:26); or in security: the adverb lavetakh is equivalent to betakh in Proverbs 1:30 and Proverbs 10:9.
The allusion is obvious. As he who is accompanied by an escort proceeds on his way in safety, so you protected by God will pass your life in security; or, as Trapp, "Thou shalt ever go under a double guard, 'the peace of God' within thee (Philippians 4:7), and the 'power of God' without thee (1 Peter 1:5)."
And thy foot shall not stumble; literally, and thou shall not strike thy foot. Stumble in the original is thiggoph, 2 singular kal future of nagaph, "to smite, … strike against with the foot." So in Psalms 91:12.
The Authorized Version, however, correctly gives the sense. The LXX; like the Authorized Version, makes "foot" the subject, ὁ δὲ ποῦς σου σὺ μὴ προσκόψῃ, "(That) thy foot may not stumble." For a similar assurance, see Proverbs 4:12.
The meaning is: You will not stumble, because you will be walking in the way of wisdom, which is free from stumbling blocks (Lapide). You will not fall into sin.