That led them through the deep, as an {o} horse in the wilderness, that they should not stumble?

(o) Peaceably and gentle, as a horse is led to his pasture.

Wesley's Notes

63:13 As an horse - With as much ease and tenderness, as an horse led by the bridle. Not stumble - That, tho' the sea were but newly divided, yet it was dried and smoothed by the wind, that God sent, as it were to prepare the way before them.

Jamieson-Fausset-Brown Bible Commentary

13. deep-literally, "the tossing and roaring sea."

wilderness-rather, the "open plain" [Horsley], wherein there is no obstacle to cause a horse in its course the danger of stumbling.

Matthew Henry's Concise Commentary

63:7-14 The latter part of this chapter, and the whole of the next, seem to express the prayers of the Jews on their conversation. They acknowledge God's great mercies and favours to their nation. They confess their wickedness and hardness of heart; they entreat his forgiveness, and deplore the miserable condition under which they have so long suffered. The only-begotten Son of the Father became the Angel or Messenger of his love; thus he redeemed and bare them with tenderness. Yet they murmured, and resisted his Holy Spirit, despising and persecuting his prophets, rejecting and crucifying the promised Messiah. All our comforts and hopes spring from the loving-kindness of the Lord, and all our miseries and fears from our sins. But he is the Saviour, and when sinners seek after him, who in other ages glorified himself by saving and feeding his purchased flock, and leading them safely through dangers, and has given his Holy Spirit to prosper the labours of his ministers, there is good ground to hope they are discovering the way of peace.