The New Testament song is the same as that sung by Old Testament saints, namely, salvation. See sweet stanzas of it, Psalms 40:3; Revelation 5:9.
Related Commentaries of Psalms 144:9
Psalms 144:9-10
9 I will sing a new song unto thee, O God: upon a psaltery and an instrument of ten strings will I sing praises unto thee.
10 It is he that giveth salvationc unto kings: who delivereth David his servant from the hurtful sword.