"Be on guard for yourselves and for all the flock, among which the Holy Spirit has made you overseers, to shepherd the church of God which He purchased with His own blood." (Acts 20:28, New American Standard Bible, emphasis added)
The Watchtower Society's rendering of Acts 20:28 is a clear example of bias to circumvent the text's implicit support for the deity of Jesus Christ. This passage has been intentionally altered by the translators to get around the fact that He is the God-man.
Following is an excerpt on Acts 20:28 from the New English Translation:
"tc The reading “of God” (τοῦ θεοῦ, tou theou) is found in א B 614 1175 1505 al vg sy; other witnesses have “of the Lord” (τοῦ κυρίου, tou kuriou) here (so P A C* D E Ψ 33 1739 al co), while the majority of the later minuscule mss conflate these two into “of the Lord and God” (τοῦ κυρίου καὶ [τοῦ] θεοῦ, tou kuriou kai [tou] theou). Although the evidence is evenly balanced between the first two readings, τοῦ θεοῦ is decidedly superior on internal grounds. The final prepositional phrase of this verse, διὰ τοῦ αἵματος τοῦ ἰδίου (dia tou haimatos tou idiou), could be rendered “through his own blood” or “through the blood of his own.” In the latter translation, the object that “own” modifies must be supplied (see tn below for discussion). But this would not be entirely clear to scribes; those who supposed that ἰδίου modified αἵματος would be prone to alter “God” to “Lord” to avoid the inference that God had blood. In a similar way, later scribes would be prone to conflate the two titles, thereby affirming the deity (with the construction τοῦ κυρίου καὶ θεοῦ following the Granville Sharp rule and referring to a single person [see ExSyn 272, 276-77, 290]) and substitutionary atonement of Christ. For these reasons, τοῦ θεοῦ best explains the rise of the other readings and should be considered authentic. sn That he obtained with the blood of his own Son. This is one of only two explicit statements in Luke-Acts highlighting the substitutionary nature of Christ’s death (the other is in Luke 22:19)."