For Robert Letham, Ephesians gets a lot of attention (he has an entire excursus on the Trinity in Ephesians).
I merely wish to point out the Trinity as we find it in Ephesians 1:3-14, specifically
The passage can be divided into three parts, one for each of the Trinity. Textually, the divides occur after vs. 6a and after vs. 12. The dividing mark is the phrase “to the praise of his glorious grace” (εἰς ἔπαινον δόξης τῆς χάριτος αὐτοῦ). This marks the end of each section (vv. 4-6a, 6b-12, 13-14). Notice that all the benefits that we have come “in Christ Jesus,” or some such variant.
The point, though, is to see just how thoroughly Trinitarian Paul is at this juncture. The blessings that we have all come from the Trinity. Ephesians 1 ought to prove just how practical this doctrine of the Trinity is: all the saving benefits that come our way come to us by way of the Trinity. From the Father we receive every spiritual blessing (ἐν πάσῃ εὐλογίᾳ πνευματικῇ), predestination not only to salvation, but also to holiness and blamelessness (ἐξελέξατο…προορίσας), and adoption (υἱοθεσίαν).
From the Son, we have received redemption (ἀπολύτρωσιν), forgiveness (τὴν ἄφεσιν τῶν παραπτωμάτων), revelation (γνωρίσας ἡμῖν τὸ μυστήριον τοῦ θελήματος αὐτοῦ), and an inheritance (εἰς οἰκονομίαν).
From the Holy Spirit, we have received the seal of the promised Holy Spirit (πιστεύσαντες ἐσφραγίσθητε τῷ πνεύματι τῆς ἐπαγγελίας τῷ ἁγίῳ), the guarantee of our inheritance. This is a “holy conspiracy” for our salvation. Let anyone who thinks the doctrine of the Trinity irrelevant, arid, scholarly, or impractical beware: he is spitting on the Scripture.