I try to think about architecture in simple terms. Architecting is about connecting the dots (physical, perceptual, conceptual, financial, and temporal).
Construction (of systems, structures, and capabilities), is focused on a fixed snapshot of dimensions (time, geography, resources, ...). Construction must work for today's needs (as we understand them from multiple stakeholders).
Architecture helps reduce the complexity of today's world (multiple dimensions amidst an accelerating pace of change) to improve the clarity for what is designed and how it should be constructed and to help ensure that the solution (whatever is constructed) can adapt to known and unknown needs of stakeholders (some call this sustainability and adaptability) over time.
The challenge with architecture has been the limited knowledge about the geometric growth in complexity and our inability to "predict" (anticipate) the needs of the stakeholders in the future. The advent of Big Data and Big Computing may help solve that, but that's probably another article or two...