Striving to keep the unity of the Spirit. σπουδάζοντες is stronger than the A.V. "endeavoring," and denotes an object to be carefully and earnestly watched for and promoted. "The unity of the Spirit" is equivalent to the unity of which the Spirit is the Author.
In all in whom he works savingly, the Spirit produces a certain oneness in faith, in repentance, in knowledge, in their views of sin, grace, Christ, the world, etc. This oneness exists, and cannot but exist, even when Christians are not careful of it, but the manifestation of it is lost; it seems to the world as if there were no such oneness.
"Many men, many minds," says the world, when believers differ much and contend much, and are at no pains to preserve and manifest the unity wrought by the Spirit. It is due to the Spirit, as well as to the interests of the kingdom of God, that the unity of the Spirit be maintained in the bond of peace.
The genitive, εἰρήυης, is commonly held to be that of apposition, the bond which consists of peace—a peace-loving spirit, a spirit laying more stress on the points in which Christians agree than those in which they differ.
Those who are combative, censorious, careless of peace, do not walk worthy of their vocation.