Having received the Most Sacred Body, and meditated for a few moments, the Priest genuflects and rises, saying:
What reward shall I give unto YHWH for all the benefits that he hath done unto me? I will receive the Cup of Salvation and call upon the Name of YHWH. At a very early point in Christian history, these words were appropriated to the Cup of the Lord's Blood; in the 'Anamnesis' of the Roman Canon the priest offers Calicem salutis perpetuae ("the Chalice of Everlasting Salvation" ... I am by no means convinced of the correctness of the assumption that the form given by S Ambrose - Calicem vitae aeternae - is earlier). Perhaps the author of the psalm had in mind the (fourth) Cup "of Blessing" in the Passover Meal; a rabbinic commentary on the psalm says: "I will elevate the chalice of salvation; that is, when I keep festival and rejoicings, I will lift up a cup of wine, I will give thanks to Him over it in the presence of many, and will make mention of the salvation wherewith He has saved me." And the probability is that this psalm (116:10ff/115) was part of the Hallel said by the Lord and His disciples on Maundy Thursday Night; in the Old Breviary it is part of Vespers on Maundy Thursdsay and Good Friday.
I will offer unto thee the sacrifice of thanksgiving and will call upon the Name of YHWH; I will pay my vows unto YHWH in the sight of all His people; in the courts of the House of YHWH, even in the midst of thee, O Jerusalem.
Protestants seem always cheerfully to have assumed that this means "Sacrifice consisting of no more than praise and thanksgiving". The phrase in the Hebrew Bible, of course, means a sacrifice, consisting, like all sacrifice, of material offerings (animal or vegetable), which are offered for a thanksgiving. Canon Arthur Couratin used drily to remark that, in the Old Testament, Sacrifices of Thanksgiving walked around on four legs. And on this Maundy Thursday it is important to remember the links in ancient sacrificial procedure ... Greek, Roman, Hebrew ... between the offering and the Sacrificial Banquet which follows the immolation and consists of eating portions of the sacrificed animal; the feast was a part of the offering. That is why it comes so easily to S Paul (I Corinthians 10:18-21) to see the Lord's Supper as sacrificial; the word he uses for supper (I Corinthians 11:29, deipnon) was used pretty well as a technical term in the invitations pagans used to send to take part in the Sacrifice and the Meal which was a integral part of the Sacrifice (many papyrus letters containing such invitations have come to light in the sands of Egypt). Some modern Christians, outside our tradition, even use the word Supper under the assumption that it points to something simple or informal or unceremonious or 'uncultic'; the contemporaries of our Lord and of S Paul would not have understood this assumption.
One also thinks here of the Levitical thank-offering of fine flour; which means that this psalm, having mentioned the Chalice, has now alluded to the two Eucharistic Elements.
This same psalm was running through the mind of whoever composed the prayer Memento, probably originally said by the Deacon and referring to the elements which the offerentes had brought up to the Altar: "who offer unto thee this sacrifice of Praise ... who render their vows ...".
These phrases have been sanctified by Eucharistic application from the Night before the Lord's Death until now. We should never forget how soaked the earliest Christians were in the Greek Old Testament*; we should never forget that we Gentile Christians are, in God's Election, Jews, grafted into God's Olive Tree so as to replace that portion of God's people which had rejected their Messiah (Romans 11:17-24).
*(After Easter, I plan to revisit some highly important teaching of Benedict XVI about the importance of the Greek Old Testament.)