The sacrifice of praise: Hebrews 13:15
By him therefore let us offer the sacrifice of praise always to God, that is to say, the fruit of lips confessing to his name.
Per ipsum ergo offeramus hostiam laudis semper Deo, id est, fructum labiorum confitentium nomini ejus.
The sacrifice of praise: Then when he says, By him them let us continually offer the sacrifice of praise to God, he presents the second conclusion, namely, that we should sacrifice upon the altar and offer certain kinds of sacrifice. For there are two kinds of sacrifice that we should offer upon Christ’s altar, namely, devotion to God and mercy towards our neighbor.
Confessing his name with our lips: ..But that sacrifice of praise is called the fruit of our lips, i.e., confession with the mouth. For God is praised better by the mouth than by the killing of animals; hence he says, the fruit of lips that acknowledge his name, for this is necessary: ‘With the heart we believe unto justice; but with the mouth, confession is made unto salvation’; ‘We will render the calves of our lips’; ‘I created the fruit of the lips’ (Is. 57:19). But this sacrifice should be offered always, i.e., continually, as there was a continual sacrifice during the Law, as it says in Numbers: ‘I will bless the Lord at all times: his praise shall be always in my mouth’.
St John Chrysostom comments on this verse:
And by Him let us offer a sacrifice to God. Of what kind of sacrifice does he speak? The fruit of lips giving thanks to His Name. They [the Jews] brought sheep, and calves, and gave them to the Priest: let us bring none of these things, but thanksgiving. This fruit let our lips put forth.
For with such sacrifices God is well pleased. Let us give such a sacrifice to Him, that He may offer [it] to The Father. For in no other way it is offered except through the Son, or rather also through a contrite mind. All these things [are said] for the weak. For that the thanks belong to the Son is evident: since otherwise, how is the honor equal? That all men (He says) should honor the Son even as they honor the Father. Wherein is the honor equal? The fruit of our lips giving thanks to His Name.
Good works: Hebrews 13:16
Meanwhile, you must remember to do good to others and give alms; God takes pleasure in such sacrifice as this.
Beneficentiæ autem et communionis nolite oblivisci: talibus enim hostiis promeretur Deus.
Works of mercy: He mentions another sacrifice, when he says, Do not neglect to do good and to share what you have. As if to say: You formerly performed works of mercy; but now at least with the heart, if you cannot in deed. Therefore, he says, Do not neglect to do good, be liberal, in regard to the things you give: ‘In doing good, let us not fail’; ‘Do good to the humble, and give not to the ungodly'. Do not forget to share what you have, i.e., the things you have saved: ‘All they that believed were together, and had all things in common’; ‘Communicating to the necessities of the saints’. Or share, namely, by charity, through which all things are common.
Merit of such sacrifices: But why should we share that double benefit is shown when he says: for such sacrifices are pleasing to God, i.e., we can merit God by such sacrifices: ‘I am your protector and your reward exceeding great’; ‘Then you shall accept the sacrifice of justice, oblations and whole burnt offerings’; ‘They shall worship him with sacrifices and offerings; and they shall make vows to the Lord and perform them’.