Jesus ..said ..Let anyone who is thirsty come to me and drink

John 7:37

37 On the last and greatest day of the festival,(B) Jesus stood and said in a loud voice, “Let anyone who is thirsty come to me and drink.(C)38 Whoever believes(D) in me, as Scripture has said,(E) rivers of living water(F) will flow from within them.”[a](G)

Isaiah 58:11

The Lord will guide(A) you always;
    he will satisfy your needs(B) in a sun-scorched land(C)
    and will strengthen(D) your frame.
You will be like a well-watered garden,(E)
    like a spring(F) whose waters never fail.

This is to be understood not of a natural thirst, though the allusion is to it, which is very painful and distressing; as the instances of the Israelites in the wilderness, Samson after he had slain the Philistines, and our Lord upon the cross, show; much less a sinful thirst, a thirst after the riches, honours, and pleasures of this life;

but a spiritual thirst, or a thirst after spiritual things, after salvation by Christ, and a view of interest in it, free and full pardon of sin through him, justification by his righteousness, a greater degree of knowledge of him, more communion with him, and conformity to him, and after the sincere milk of the word,..

and such that thirst after these things, and eagerly desire them, and are in pain and uneasiness without them, as a man is, who has a violent thirst upon him, are such as are regenerated and quickened by the Spirit of God, and are made sensible of themselves, and of their state and condition by nature. 

Now these Christ invites to come unto him, not to Moses and his law, moral or ceremonial, and to obedience to them, and works of righteousness done by them, to any creature, or creature acts; for these are cisterns without water, where no true peace, joy, righteousness, and salvation are to be had; but to himself, who is the fountain of gardens, the well of living waters, and who is as rivers of water in a dry land, to thirsty souls: 

and when come to him, which is by believing in him, they are encouraged to drink; 

that is, to take of the water of life freely, or to take of his grace freely; salvation by him is of free grace, and the pardon of sin is according to the riches of grace, and justification is freely by his grace, and so all other blessings; and of this they may drink abundantly, or they may partake of it largely: 

there is a fulness of grace in Christ, and there is an abundance of it communicated to his people; it is exceeding abundant; it flows, and overflows, and may be drank of to satisfaction, till their souls are as a watered garden, and they are satisfied with the goodness of the Lord.

Gill exposition