God is an infinitely perfect being because in Him there is no limitation of any kind. God is an infinitely perfect spiritual being, without beginning or end. He knows and loves without limit.
Angels and men are also spiritual beings, but being creatures, they are limited or finite. Consequently, their perfections are limited.
Angels are pure spirits, meaning that they have no bodies. Men are both spiritual and material. They have material bodies and spiritual souls. Being spiritual, angels and men have minds and wills. They can know and love, but only to a limited degree. God alone is the infinitely perfect being. He is the infinitely perfect Spirit.