The inadvertent loss of the propers is the great tragedy in the Ordinary Form, but the Offertory chant in particular is even more lost than the others, sung by almost no parish apart from a few models and ideals. Truly, there is no reason for this. The chant still appears in the Graduale, which remains the music book of the Roman Rite. Moreover, GIRM #74 specifies it: "The procession bringing the gifts is accompanied by the Offertory chant."
It is a grimly sad loss when you consider a masterpiece such as the Offertory chant for this Sunday, the 25th in ordinary time. The text is "If I walk in the midst of tribulation you shall preserve my life, O Lord; you shall stretch forth your hand against the fury of my enemies; your right hand has delivered me."
Now, keep in mind the character of the Offertory chant. It combines the forward motion of the Introit (because it too is a procession) with the melismatic properties of the typical Gradual (because it too is a Psalm and is constructed to inspire reflection) to create some of the most picturesque and artistically evocative chants of the entire songbooks of the Roman Rite.
In this chant, we have a story that is well suited to composition. We have a walk in distress. We have the hand of God, and it is stretching forth. That hand is raised against enemies, and protects the believer, delivering him from them. How might this chant look? I submit that you could work years and not come up with some as spectacular as the following.
You can literally see what is happening here, and to hear it in liturgy would be to experience Psalm 137 in a way that would be otherwise impossible. The excitement emerges from the start and grows into one long phrase that culminates in this incredible melisma on the word life itself. The next long melisma occurs on another phrase you might expect it: extendes manum, the stretched forth hand, and here the chant reaches its highest melodic peak. But the sense of life and stretching doesn't end there. It continues to the third great melisma of the piece, which is on the words dextera tua. Putting them together we have the bulk of this chant consumed with a long life made possible by the hands of God.
It's great composition, even aside from its liturgical intention of preparing for the sacrifice at the altar.
Dom Johner comments: "Logically the first and second phrase belong together; they should therefore not be separated by too great a pause. Beginning and end of the two phrases are alike. In these two phrases, as well as in the later ones, we meet numerous fourths. These give life and buoyancy to the piece. To this must be added the strengthening of (vivifi)-cd-(bis), which gives added impressiveness to our Amen. The third phrase has a beginning similar to the first, descending like it to low d. We are acquainted with the melody over extendes from the Offertory of Easter Monday: Surrexit. In the spirit of Easter, confident of victory, the singer bursts out into a joyous strain over manum tuam. He knows what it means to have God's almighty hand resting upon him. Tuam calls for a continuation. The simple recitative et salvum me which follows, set as it is in the midst of a florid melody, has an especial solemn character and must not be sung too rapidly. Over tua the melody is to be divided into two bistrophas and a clivis, followed by an energetic pressus."
It is possible to still sing the Offertory proper even if you aren't prepared to sing the symphonic version above. Here is a setting from the Anglican Use Gradual that puts it in a Psalm tone that any choir can sing. This is a good idea. Singing the proper helps takes this period of Mass from having the feel of an intermission into making it part of the liturgical structure of the day.