73 The demonstrative “this” refers back to the hope just mentioned or forward to the statement in the second line concerning the promise’s power to revive. See the note on the word “me” at the end of the verse for further discussion.
74 The hope generated by the promise (see v. 49b) brings comfort because (note “for” at the beginning of the line) the promise revives the psalmist’s spirits. Another option is to take כִּי (ki) at the beginning of the second line in the sense of “that,” in which case “this” refers to the promise’s power to revive.

In other versions

Remember your word to your servant,

in which you have made me hope.

This is my comfort in my affliction,

that your promise gives me life.

Remember your word to your servant,

for you have given me hope.

My comfort in my suffering is this:

Your promise preserves my life.

Remember your word to your servant;

you have given me hope through it.

This is my comfort in my affliction:

Your promise has given me life.

Remember your promise to me;

it is my only hope.

Your promise revives me;

it comforts me in all my troubles.

Remember your word to your servant,

upon which you have caused me to hope.

This is my comfort in my misery:

that your word preserves my life.

ZAIN.

Remember the word unto thy servant,

Upon which thou hast caused me to hope.

This is my comfort in my affliction:

For thy word hath quickened me.

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